Keston C90, C110 User Manual

WD352/0/2003 The Keston C90 & C110

Fan Powered High Efficiency

Modulating Commercial Condensing Gas Boiler

Installation And Servicing Instructions

C90 and C110 Models

CE/PI No : 87BN14

These instructions must be left either with

the user or next to the site gas meter.

34 West Common Road

Hayes, Bromley,Kent BR2 7BX

Tel. [phone] Fax. [phone]

email : [e-mail] web : www.keston.co.uk

COMPLIANT WITH BUILDING REGULATION PART L2 2002

WD352/0/2003 The Keston C90 & C110

CONTENTS

Section Description

0 HANDLING INSTRUCTIONS

0.1 List of contents

0.2 Recommended handling procedure

1 GENERAL INSTRUCTION

1.1 Description

1.2 Boiler Schematic

1.3 Related Documents

1.4 Physical Data

1.5 Performance Data C90

1.6 Performance Data C110

1.7 Optional Accessories

2 BOILER LOCATION

2.1 Dimensions & Minimum Clearances

2.2 Service Connections

2.3 Position

2.4 Electrical

2.5 Boiler Size Selection

2.6 Gas Supply

2.7 Water Systems

2.8 Flue System

2.9 Air Supply

2.10 Compartment Installation

2.11 Condensate Drainage

3 INSTALLATION OF THE BOILER

3.1 Wall Mounting Bracket

3.2 Mounting The Boiler

3.3 Floor Standing - Optional

3.4 Assembly Practice

3.5 Installing Flue And Air Pipes

3.6 Condensate Drainage

3.7 Water System

3.8 Gas Supply

3.9 Electrical Supply

3.10 Exchanging A Boiler

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WD352/0/2003 The Keston C90 & C110

4 COMMISSIONING OF THE BOILER

4.1 Initial Flushing

4.2 Gas Supply

4.3 Electrical Installation

4.4 Initial Firing

4.5 Hot Flushing

4.6 Combustion Testing

4.7 Checking The Gas Pressure

4.8 Timing The Gas Meter

4.9 Handing Over To The User

5 FAULT FINDING

5.1 Electrical Control Sequence

5.2 Normal Operation

5.3 Fault Modes

5.4 Functional Flow Wiring Diagram

5.5 Electrical Wiring Diagram

5.6 Illustrated Wiring Diagram

5.7 Exploded Assembly Diagrams

6 SERVICING

6.1 Pre Service Checks

6.2 Recommended Routine Module Service

REPLACEMENT OF PARTS

7.0 General

7.1 Precautions

7.2 Access

7.3 Replacement Procedure

7.4 Electrical Components

7.5 Spark Ignition/Flame Detection Electrode

7.6 Burner

7.7 Heat Exchanger

7.8 Condensate Trap

7.9 Pump

8 SPARE PARTS LISTINGS

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WD352/0/2003 The Keston C90 & C110

0. HANDLING INSTRUCTION

0.1 LIST OF CONTENTS

The Keston C90 and C110 are supplied almost totally pre-assembled. Since the units use 100
mm Keston Composite pipe for the flue and air intake systems the boiler is packed in a single
box without additional flue kit. All additional components are packed inside the boiler cabinet
itself. The following is a list of components and their location in the boiler cabinet

Equipment List
Item Quantity Location
Wall Bracket Rawl Plugs 9 Inside accessories bag
Wall Bracket Wall Fixing Screws 9 Inside accessories bag
Wall Mounting Bracket 1 Over the boiler case
100 mm Air/Flue Terminals 2 Inside the boiler case
Cabinet Cable Entry Clamps 4 Inside accessories bag
User Control Knobs 2 Inside accessories bag
Boiler Lifting Handles 2 Over the boiler case

Document List
Item Quantity Location
User Instructions 1 In A4 envelope
Registration of Purchase 1 In A4 envelope
Installation Template 1 In document bag

Remove the cabinet door by removing the two retaining screws in the top of the cabinet front
panel and lift the front panel away from the cabinet.

0.2 Recommended Handling Procedure CAUTION - HEAVY UNIT - MULTI-PERSON LIFT

When ready to hang the boiler on the wall stand the boiler on its base and insert the lifting
handles in each side of the boiler. At this stage it is assumed that the wall bracket is correctly
secured on the wall face.

a) The boiler has a dry weight of 127 kg (280 lbs) and will therefore require at least four

people to lift without the use of lifting aids.

b) Lift the boiler using the lifting handle inserted into each side of the boiler. When lifting this

appliance the back should be kept straight at all times. Avoid twisting at the waist ­reposition the feet instead. Avoid upper body bending when holding the appliance and
keep the boiler as close to the body as possible.

c) Lift the boiler and locate onto the wall mounting bracket ensuring the lip on the back of the

boiler cabinet engages fully with the wall bracket.

Safety footwear and gloves are recommended PPE when lifting this appliance.

The C90 and C110 boilers can be fitted in compartments with very small clearances required
around the appliance (refer to Section 2.1). Due consideration should therefore be given to
access within the compartment for lifting and positioning.

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WD352/0/2003 Chapter 1 : General Instruction The Keston C90 & C110

1. GENERAL INSTRUCTION

1.1 DESCRIPTION

The Keston C90 and C110 are unique in concept and design. They comprise two high
efficiency stainless steel heat exchangers coupled with low emissions burners to deliver
ultra high efficiency condensing mode operation within a compact wall hung cabinet. The
unit automatically adjusts gas and air rate according to demand to give an output in the
range of 22kW to 90kW (C90) and 25kW to 110kW (C110). The integral Grundfos pumps
are automatically controlled to best match water flow rate to heat output & further increase
appliance efficiency. In addition, the boilers feature an optional connection for an outside
sensor to enable the boilers inbuilt weather compensation option. Separate inputs are
provided for hot water and central heating demand signals to enable different temperature
levels to be set (ideal for underfloor heating systems). The boiler features two sets of flow
and return tappings to enable these two temperature levels to be supplied simultaneously.
Common applications for this technology are weather compensated heating in conjunction
with high temperature flow for DHW production. While the application for which the C90
and C110 were designed is the same as those which other boilers are used, the Keston
C90 and C110 have the added advantage of very high efficiency, and small diameter
plastic flue which can be extended up to 30m metres horizontally or vertically.

The Keston C90 and C110 uses a variable speed combustion blowers to deliver a premix
of gas and air to a downward firing burners in high efficiency, single pass heat
exchangers. The flue system is room sealed and fan powered. The ignition is direct spark
and fully automatic. The boiler housing is not waterproof and should be installed in a
position where it will always be dry. Combustion air is drawn from the cabinet which is
connected to outside atmosphere via a plastic intake pipe. The cabinet therefore remains
under negative pressure at all times the boiler is operating.

The boiler is suitable for connection to open vented or, preferably, sealed systems.

The boiler has two heat exchangers. They are made from highly corrosion resistant
stainless steel in corrugated pipe form which provides massive surface area within a
compact dimension. The hot combustion gases from the down firing burner pass around
the stainless steel pipes imparting heat into the system water. The integral variable speed
Grundfos pumps within the appliance cabinet ensures the heat exchanger receives
correct water flow when firing. The C90 and C110 are not high water content boilers and
do not contain the metal mass, or water volume, of a cast iron or steel boiler. The boiler is
of low mass and low water content and therefore responds faster when there is a call for
heat. The C90 and C110 feature full user diagnostics, integral frost protection function,
automatic pump and fan exercise in periods of inactivity, anti cycle control, dry fire
protection and connections for remote lockout and run monitoring (optional accessory).

1.2 BOILER SCHEMATIC

Air is drawn into the boiler through a 100 mm Keston Composite plastic pipe. Gas is
mixed with combustion air at the inlet to the fan. The gas flow is automatically regulated by
the gas valve according to the air flow generated by the fan. The gas and air are
thoroughly mixed in the blower and fed into the burner located at the top end of the heat
exchanger module. The gas and air mixture is ignited by a direct spark ignition control
system and burns with a blue flame just off the surface of the burner. As the hot products
of combustion pass downwards, they are cooled by exchanging heat with the circulating
water which enters the heat exchanger at the bottom of the heat exchanger. The optimum
heat input is detected by monitoring flow and return temperatures and is adjusted by
controlling the speed of the fan. The optimum pump speed is also detected and
automatically selected by the boiler.

When the return water temperature is below 55oC, part of the water vapour in the
combustion products will condense inside the heat exchanger, thus increasing the boiler
efficiency further by releasing the latent heat of condensation. This condensate falls to the
bottom of the heat exchanger where it is separated from the flue gases and exits from the

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WD265/0/2002 Chapter 1 : General Instruction The Keston C90 and C110

boiler through the condensate drain. Any condensate formed in the flue runs back down
the flueway and is drained at the base of the flue connection to the heat exchanger or
drain points within the flue.

1 2 3 4 5 6 7 8 9

LEGEND

1 Gas Valve
2 Mixing Venturi
3 Combustion Blower
4 Module Control Box
5 Ignitor
6 Auto Air Vent
7 Flue Check Valve
8 Air Inlet
9 Flue Header
10 User Control Panel
11 Main Return Connection
12 Module Pump
13 Gas Connection
14 Condensate Trap
15 Gas Cock
16 DHW Return Connection

10 11 12 13 14 15 16 17 18 19 20

17 Check Valve
18 DHW Flow Connection
19 Diverter Valve
20 Main Flow Connection

Fig. 1.2 - Boiler Layout

The condensate is very slightly acidic (about the same acidity as vinegar) and should be
piped in a plastic pipe. It is not harmful to the waste disposal system and may be disposed
of as normal waste water.

The flue gases are piped in a 100 mm Keston Composite pipe. The temperature of the
flue gases are usually around 5oC to 10oC above the temperature of the return water. The
flue pipe should be terminated outside the building from where they cannot re-enter the
building or any other adjacent building.

The heating level may be controlled by room thermostats, hot water calorifier thermostats,
programmer time clocks and energy management systems.

The C90 and C110 feature an integral frost protection function which will operate the
pump, regardless of the external controls, should the boiler temperature fall below 7oC. In
the event the boiler temperature falls below 3oC the boiler will also fire. This is to avoid
damage to the boiler through freezing of boiler water. The boiler will turn off when the flow
temperature exceeds 10oC.

The C90 and C110 feature an integral pump exercise function which will run the module
pumps, without firing the boiler, for 10 seconds in the event the boiler is on standby for in
excess of 24 hours without firing. This is to help prevent seizing of the pump due to long
periods of inactivity.

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WD352/0/2003 Chapter 1 : General Instruction The Keston C90 & C110

1.3 RELATED DOCUMENTS

The Keston C90 and C110 Condensing Boiler must be installed in accordance with the
current issue of the Gas Safety (Installation and Use) Regulations 1996, current IEE
Wiring Regulations, Building Regulations, Building Standards (Scotland) Consolidation,
and the Bye Laws of the local Water Undertaking.

In addition, due account must be taken to the following Codes Of Practice:

BS 6891 : Gas Supplies
BS 6644 : Installation of gas fired hot water of rated input between

60kW and 2MW
BS 6880 : Central Heating by LPHW
BS 7593 : Treatment of Water in Hot Water Central Heating

Systems
CP342.2 : Centralised HW Supply
IM/2 : Purging procedure for non-domestic gas installations
IM/16 : Guidance for installation of gas pipework boosters and

compressors for customers premises
IM/22 : Installation guide for high efficiency (condensing) boilers
(industrial and commercial appliances)
For Timber Framed Buildings please refer to The Institute of Gas Engineers
document IGE/UP/7:1998.

1.4 PHYSICAL DATA - C90 and C110

Cabinet Height mm 825
Cabinet Width mm 1000
Cabinet Depth mm 337
Top Clearance mm 350
Side Clearance mm 25
Base Clearance mm 150
Front Clearance (for servicing) mm 300
Weight - Full kg / (lbs) 147 / (324)
Weight - Empty kg / (lbs) 127 / (280)
Flow and Return Connection Rp 1.5" F
DHW Connection Rp 1” F
Gas Connection Rp 1" F
Condensate Connection mm 22mm plastic overflow
IP Rating IP20 (IPX0)

Flue and Air Intake Material 100mm Keston Composite
Flue Pipe Size (nominal bore) mm / (in) 100 / (4)
Air Intake Pipe Size (nominal bore) mm / (in) 100 / (4)
Max. Air Intake Length m 59
Max. Flue Outlet Length m 30
Max. Total Flue Outlet and Air Intake Length m 60

Keston Boilers Ltd declare that there are no substances harmful to health within the
appliance or used during the production of the appliance.

The C90 and C110 are intended for domestic and commercial EMC environments and on a
governed G20 meter supply.

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WD265/0/2002 Chapter 1 : General Instruction The Keston C90 and C110

1.5 PERFORMANCE DATA - C90

Max. Input (Gross CV) kW/(Btu/h) 91.2 (311,200)
Min. Input (Gross CV) kW/(Btu/h) 25.8 (88,000)
Max. Output To Water

(80/60oC Flow/Return) kW/(Btu/h) 79.9 (272,500)
(50/30oC Flow/Return) kW/(Btu/h) 89.8 (306,800)
Min. Output To Water

(80/60oC Flow/Return) kW/(Btu/h) 22.6 (77,000)
(50/30oC Flow/Return) kW/(Btu/h) 25.2 (86,000)
Max. Burner Press.-Hot (Factory Preset) mbar/(in w.g) 0
Gas Consumption After 10 mins l/s / (Ft3/hr) 2.414 (307)
Max. Operating Flow Temp.

o

C 82
Max. Head (Open Systems) m / (ft) 30.5
Max. Press. (Sealed System) bar 2.70
Min. Head (Open Systems) m 3.0
Inlet Gas Pressure mbar/(in w.g) 20

Recommended Temp Diff.

o

C 8 to 20
Electrical Supply 230V 50Hz
Power Consumption (Max) W 520
Power Consumption (Standby) W 16
Type of Gas G20 Natural Gas
Optimum Flue Gas CO2 Level % 8.3
Expected CO/CO2 Ratio (at max rate) 0.001
Destination Countries GB/IE

1.6 PERFORMANCE DATA - C110

Max. Input (Gross CV) kW/(Btu/h) 113.0 (385,600)
Min. Input (Gross CV) kW/(Btu/h) 28.6 (97,500)
Max. Output To Water

(80/60oC Flow/Return) kW/(Btu/h) 99.4 (339,400)
(50/30oC Flow/Return) kW/(Btu/h) 110.4 (377,000)
Min. Output To Water

(80/60oC Flow/Return) kW/(Btu/h) 25.0 (85,300)
(50/30oC Flow/Return) kW/(Btu/h) 28.6 (97,500)
Max. Burner Press.-Hot (Factory Preset) mbar/(in w.g) 0
Gas Consumption After 10 mins l/s / (Ft3/hr) 2.992 (380)
Max. Operating Flow Temp.

o

C 82.00
Max. Head (Open Systems) m / (ft) 30.5
Max. Press. (Sealed System) bar 2.70
Min. Head (Open Systems) m 3.0
Inlet Gas Pressure mbar/(in w.g) 20.0 / (8.0)

Recommended Temp Diff.

o

C 8 to 20
Electrical Supply 230V 50Hz
Power Consumption (Max) W 520
Power Consumption (Standby) W 16
Type of Gas G20 Natural Gas
Optimum Flue Gas CO2 Level % 8.8
Expected CO/CO2 Ratio (at max rate) 0.001
Destination Countries GB/IE

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WD352/0/2003 Chapter 1 : General Instruction The Keston C90 & C110

IMPORTANT
This product contains ceramic fibre boards, which although not regarded as a risk, contain
ceramic fibre which may cause temporary irritation to eyes, skin and respiratory tract. The
fibres are held in place by inorganic binders. Therefore as long as the boards are not
disturbed they will not be released. Since the boards are non-serviceable parts there
should be no risk.

To ensure that the release of fibres from these RCF articles is kept to a minimum, during
installation and servicing we recommend that you use a HEPA filtered vacuum to remove
any dust accumulated in and around the appliance before and after working on the appli­ance. When replacing these articles we recommend that the replaced items are not broken
up, but are sealed within heavy duty polythene bags, and clearly labelled as RCF waste.
RCF waste is classed as a stable, non-reactive hazardous waste and may be disposed at a
landfill licensed to accept such waste. Protective clothing is not required when handling
these articles, but we recommend you follow the normal hygiene rules of not smoking,
eating or drinking in the work area and always wash your hands before eating or drinking.

CORGI CONTACT INFORMATION

The boiler should be installed and serviced only by CORGI registered operatives. All CORGI
registered Installers carry a CORGI ID card, and have a registration number. You can call CORGI
direct on 01256 372300.

1.7 OPTIONAL ACCESSORIES

A range of accessories are available from Keston Boilers Ltd to compliment an installation.

Description Part Number

Outside Temperature Sensor C.34.0.07.00.0
Floor Standing Support Frame C.34.0.06.00.0

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

All dimensions in mm.

2. BOILER LOCATION

350

2.1 DIMENSIONS AND MINIMUM
CLEARANCES

The boiler must be installed in minimum
clearances shown to allow subsequent
servicing, and safe operation. However,
larger clearances may be required during
installation.

2.2 SERVICE CONNECTIONS

Gas, water, air and flue pipe, condensation,
and electrical connections are as shown.
Gas : 1 inch BSP female. Flow/Return 1.5

inch BSP female. DHW/Zone 2 connection 1
inch BSP female

2.3 POSITION

The C90 and C110 are not suitable for
external installation. The boiler may be
installed in any room or internal space,
although particular attention is drawn to the
requirements of the current IEE Wiring
Regulations and, in Scotland, the electrical
provisions of the Building Regulations
applicable in Scotland, with respect to the
installation of the boiler in a room or
internal space containing a bath or shower.
Where a room-sealed appliance is installed
in a room containing a bath or shower, any
electrical switch or appliance control,
utilising mains electricity, should be so
situated that it cannot be touched by a
person using the bath or shower. The C90
and C110 are classified as IP20 (IPX0).
The wall on which the boiler is mounted
must be of suitable load bearing capacity
and must be non-combustible.

Figure 2.1.2
Dimensions

Air Intake

Flue

2525

305 (when servicing appliance)
10 (When appliance is operating)

150

All dimensions in mm.

7

3

3

1000

825

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

Compartment installation is permitted. Such compartments must be constructed in
accordance with BS6798.

IMPORTANT : It is not recommended to install the boiler on a studded wall or similar. It is
possible that vibration from the boiler could be amplified and transmitted to other parts of
the property.

The Keston C90 and C110 can be located virtually anywhere desired provided that all
regulations are complied with. Because of the boiler's compact size and venting flexibility,
the installation is not limited to a boiler room setting. Before locating the boiler near a living
space consider whether the sounds generated by the boiler will be objectionable. The
boiler may be located within a cupboard enclosure to reduce noise levels if located within

a living space.

2.4 ELECTRICAL

2.4.1 Electrical Connections

The boiler must be connected to a permanent 230V ~ 50Hz supply, fused at 5A.

The boiler has two thermostats and will therefore accept up to two switched
live signal inputs at 230V, such as heating and hot water demand. For
single signal systems switched live 1 may be used on its own. When
serving a demand from switched live 1 only, both burner modules are
assigned to serving the demand at the required temperature setpoint. In the
event the boiler receives a signal from switched live 2, burner module 1 is
diverted away from the main flow output and onto the DHW flow output.
Burner module 1 will then produce heat to satisfy the heat demand on
switched live 2 at the temperature setpoint requested on thermostat 2. In
the event a demand is receive simultaneously from switched live 1 and 2
the boiler will service both demands at the two different setpoints. Wiring

external to the boiler must be in accordance with current I.E.E wiring regulations
and local regulations.
The method of connection to the mains electricity supply must facilitate complete
electrical isolation of the boiler, preferably by the use of a fused, unswitched three
pin plug and a shuttered socket-outlet, both complying with the requirements of
BS 1363. There must be only one common method of isolation for the boiler and
its control system.
The appliance must be connected to the 5A supply via a fused double-pole switch
having at least 3 mm (1/8 inch) contact separation in both poles, serving only the
boiler and the system controls.
The connection point to the mains supply should be readily accessible and
adjacent to the boiler, except for rooms containing a bath or a shower. Refer to
section 2.3 Position.

2.4.2 External Wiring & Controls

1. The boiler is designed so that all control wiring is external to the boiler.

2. A programmer may be used with zone valves to give independent control
of central heating and hot water.

3. Control signal inputs must the 230VAC "switched live" type.

4. A Keston 90/110 outside temperature sensor may be connected as an
option. The boiler will automatically detect this connection and will operate
on a "weather compensation" basis when receiving a signal on switched
live 1. Screened cable (80% density, 4-core) must be used to connect the
outside temperature sensor.

Installation & Servicing Instructions Page : 7

WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

Brown

V4043H1106
Zone Valve
Heating

V4043H1056
Zone Valve
DHW

2.4.4 Wiring Example - Honeywell S-Plan for DHW and (Optional) Weather Compensated Heating Control

Blue

Grey

Orange

Green/Yellow

White

Brown

Blue

Grey

Orange

Green/Yellow

5
2
1
9
3
N/U

8
2
1
10
3

Cyl. Thermostat
L641A1039

2.5 BOILER SIZE SELECTION

The C90 and C110 will automatically adjust heat output and pump speed to match the
system requirements at any given time. Efficiency and combustion levels are maintained
at optimum levels throughout the possible output range. The C90 and C110 are therefore
suitable for all systems with a total heat load within the maximum range of the boiler.
However, when serving a demand on switched live 2 the available power to the switched

live 1 demand is halved.

Mains Supply
Fused @ 3A

230V

Programmer
ST6300A

L
N

E
SL1
SL2
EX1
EX2
EX3
EX4

Keston Spa
Cylinder Stat

Keston Spa
Overheat Stat

1
3
2

Live

Neutral

Earth

L
N
1
3
4

C
1
2

1
2
3

1
2

6
4

6
8

Room Thermostat
T6360B1028

KESTON
C90 / C110

OR

C
1
2

C
1
2

4
5
2

1
2
3
9
10

To Keston
Ext. Sensor
[Optional]

6

8

2.6 GAS SUPPLY

A gas meter should be connected to the service pipe by the local gas region or their
contractor. An existing meter should be checked preferably by the gas region to ensure
that the meter is adequate to deal with the rate of gas supply required. Installation pipes
should be fitted in accordance with BS 6891.

Minimum/Maximum Gas Pressure:

Natural gas pressure before the gas valve must be maintained at between 18 mbar (7.2 in
WG) and 22 mbar (8.8 in) while the boiler is running.
Gas pressures above or below these levels will lead to problems associated with the gas
valve's internal pressure regulator.

Supply pipes to the boiler must not be sized less than the boiler inlet connection
(28 mm). Due consideration must be given to the supply pressure to other gas
appliances in the premises. Reduction in dynamic gas supply pressure will result in
intermittent ignition failures. Ensure gas supply pipe work is adequately sized for
the length of run from the meter to the boiler at a supply rate of 92kW for the C90
and 114kW for the C110 model.

2.7 WATER SYSTEMS

All piping must be installed in accordance with all applicable local and Water Supply
Bylaws for forced hot water heating systems.
Consideration must be given to pipe capabilities and pressure drop through the piping
when selecting pipe sizes. The primary pipe connections to the boiler must be sized

according to the system load, not dictated by the boiler connection sizes.

Water treatment must be carried out to BS 7593 : Treatment of Water in Hot Water
Central Heating Systems.

a. The C90 and C110 are suitable for use on open, vented water systems with

combined feed and vent of 32mm nominal diameter fitted to the boiler return.

b. It is preferable for use on sealed water systems, provided the appropriate

components required (see Section 2.7.2 Sealed Systems) are included in the
system.

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

c. Any system must be thoroughly flushed clean of grease, dirt and debris, prior to

connection with the boiler. A trap may be installed in the flow line to collect any
solder, or other debris, from the installation.

d. All water systems must be constructed to comply with requirements of the Local

Water Authority.

e. Jointing should be either with capillary, threaded or compression fittings. Pipes

should have a gradient to ensure air is passed easily to vent points and water
flows readily to drain points.

f. Draining taps must be located in accessible positions which permit the draining of

the boiler and hot water storage vessel. Draining taps should be at least 22 mm in
nominal size and be in accordance with BS 2879.
AIR VENT POINTS

g. These must be fitted at all high points where air will naturally collect and must be

sited to allow complete draining of the system.

h. Where thermal stores are to be used the thermal store supplier should be

consulted as to the compatibility of the thermal store with a Keston C90 and
C110. Thermal store units where the boiler directly heats an open vented thermal
store are not suitable for use with the C90 or C110.

2.7.1 Open Vented Systems

A typical system is shown in Figure 2.7.1 which includes a combined feed and
vent. Note that the combined feed and vent must be fitted to the primary
RETURN. Note that the valve between the boiler flow and the open vent is a three
way blowdown type valve. Note that the minimum static head required is 3m at
the top of the boiler. If the cold feed/vent is not brought to the low loss header as
shown then the pressure loss across the heat exchangers may have to be taken
into account when estimating the static pressure. Cold Feed/vent size must
comply with BS6644.

Expansion
Pipe

Boiler

KESTON

R R F F

CV

3 Way
Valve

IV

Drain

32mm
Min.
dia.

IV

Low loss
header

IV

DOC

Expansion
Tank

Minimum
3m Height

Pump

Strainer

IV

IV

Figure 2.7.1
Open Vented System

System
flow(s)

AAV

32mm
Pipe

System
return(s)

Cylinder

DOC

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

Although suitable for open vented systems with combined feed and vent
arrangements, the C90 and C110 are low water content boilers. As such, any air
entrainment within the system water will produce boiler “kettling”. It is therefore
recommended, if in any doubt, to consider the use of sealed systems where
possible.

2.7.2 Sealed Systems

Sealed systems must be designed in accordance with BS 6644 and BS 7074 Pt1.
A typical sealed system is shown in Figure 2.7.2. It must include :

(i) A safety valve fitted on the flow, adjacent to the boiler. It must be non

adjustable and preset to 3 bar. A drain pipe must be attached, at least as
big as the valve connection, and routed to drain in any area not
hazardous nor where it may be subject to freezing.

(ii) An expansion vessel complying with BS 4814 and sized in accordance

with the requirements of BS 5449 and BS 7074 Pt 1. The vessel must
be positioned on the primary return to the boiler. Table 2.7.2
Expansion Vessel Selection provides guidance for the correct expansion

vessel size to use.
(iii) A filling point, in accordance with local water authority requirements.
(iv) A method of system make-up (automatic or manual), in accordance with

local water authority requirements.
(v) There must be no permanent connection of mains water to the boiler

system.
(vi) The installation must be designed to work with flow temperatures of up to

110 oC.

Safety Valve

Cylinder

Boiler

KESTON

Expansion
Vessel

Safety Valve

FR R

F

CV

DOC

IV

IV

AV

IV IV

Low loss
header

IV IV

DOC

Pump

Strainer

System flow(s)

System return(s)

Fill Point

Expansion
Vessel

Figure 2.7.2
Sealed System

All components of the system including the heat exchanger of the indirect cylinder
must be suitable for a working pressure of 3 bar and a temperature of 110 oC.
Care should be taken in making all connections that the risk of leakage is
minimised.

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

Safety Valve Setting
Vessel charge & initial system

pressure.

25 litres
50 litres
75 litres
100 litres
125 litres
150 litres
175 litres
200 litres
225 litres
250 litres
275 litres
300 litres
Multiplying factor for other system
volumes

Table 2.7.2 Expansion Vessel Selection

2.7.3 Hot Water System (if applicable)

The hot water storage vessel must be of the indirect type. DIRECT CYLINDERS
MUST NOT BE USED. Further guidance is provided in BS 1394.

The Keston Spa range of stainless steel unvented cylinders are an ideal
option for use with the Keston range. The Keston Spa range combine
exceptional recovery times with durable, long life stainless steel
construction and all associated controls. Contact Keston Boilers Ltd for
information

3.0 bar

1.5 bar1.0 bar0.5 bar

VolumeVessel ExpansionTotal Water Content of system

3.92.72.1

7.85.44.2

11.78.26.3

15.610.98.3

19.513.610.4

23.416.312.5

27.319.114.6

31.221.816.7

35.124.518.7

39.027.220.8

42.930.022.9

46.832.725.0

0.1560.1090.0833

2.7.4 Balance Headers - Multiple Boiler Installations

Boiler water flows are critical to the operation of the boiler. If flow cannot be
maintained through the system pipework to maintain the minimums required by
the boiler, the boiler will “kettle” or even produce steam which can damage the
heat exchanger and will invalidate the heat exchanger warranty. The
implementation of a balance header, as shown in the above schematics, is
required to ensure adequate circulation is maintained through the boiler by the
integral shunt pumps, regardless of system conditions.

The size of the balance header is dependant on the number of boilers serving the
header. A guide to sizing is given below:

Total Boiler Output (Max) Header Diameter
Up to 110kW 3”
Up to 220kW 4”
Up to 330kW 4.5”
Up to 440kW 5”

When assembling the balance header the following design considerations must
be observed:
A) Each boiler must have its own flow and return connections to the balance

header pipe. Common flow and return connections with the other boilers
will cause reverse circulation effects to occur.

B) The minimum distance between the system flow and return connections

is 600mm.

C) A drain off point should be fitted to the base of the header, along with

cleaning access, for sludge removal.

D) The top of the header should be vented.

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

Static Pressure - m WC

2.7.5 Air Elimination

In the initial charge of water to the boiler system and in all subsequent additions
of water to the system some air will be dissolved in the water. As the water is
heated the air is driven out of the solution and will collect in high spots in the
system. These air bubbles can interfere with pumping and heat transfer and

must be eliminated.

Installation of air bleed valves at the high spot(s) in the system will allow for air
elimination when filling the system and will allow re-venting in a day or so after all
air has been driven out of solution.

2.7.6 System Pump Selection
The C90 and C110 feature integral
circulating pumps which have
sufficient excess head to drive
through the balance header.
However, a system pump will be
required to provide circulation of
water from the balance header,
around the system. This system
pump should be selected to provide
the required system flow rate at the
pressure drop created by the index
circuit.

2.8 FLUE SYSTEM

2.8.1 Design

Individual air supply and flue outlet
pipes are used. The material used
for flue outlet &/or air inlet must be
Keston Composite Pipe of an
internal diameter of not less than
100mm. Suitable pipe and fittings
can be obtained from Keston Boilers
Ltd via its appointed distributors.

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

40 60 80 100 120

20

Water Flow - L/min

Fig 2.7.6 Available Pump Head Graph

Both flue outlet terminal and air inlet
terminal are supplied and are illustrated in Figure

2.8.1. Both terminals are identical.

.

Although both terminals are identical great care

must be taken to ensure that the air intake is
positioned in such a way as to ensure rain cannot
enter the air intake pipework. Boiler damage due
to water entry through the air intake pipework is
not covered under the appliance warranty.

2.8.2 Maximum Lengths

The maximum lengths of both air inlet pipe and
flue outlet pipe, when no bends are used, are as

Flue Outlet/Air Inlet Terminals

Figure 2.8.1 : Terminals

detailed below.

Minimum Flue Length : 0.5m
Minimum Air Intake Length : 0.5m
Maximum Air Inlet Length : 59.0 m
Maximum Flue Outlet Length : 30.0 m
Maximum Total Flue and Air Intake Length : 60.0 m

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WD352/0/2003 Chapter 2 - Boiler Location The Keston C90 & C110

However, each bend
used has an
equivalent length that
must be deducted

AIR

FLUE

from the maximum
straight length stated
above. Knuckle
bends must not be
used.
A 92.5o sweep

elbow is equivalent to 1.0m straight

b

a

C90 / C110

d

c

length.

Example

Air inlet uses two one

92.5o sweep elbows.
Hence, maximum
length permissible

Figure 2.8.2 : Flue & Air Maximum Length Example

(i.e. a+b in figure

2.8.2) = 59.0m - 1.0m - 1.0m = 57.0m

Flue outlet uses one 92.5o sweep
elbow. Hence, maximum length
permissible (i.e. c+d in figure 2.8.2)
= 30.0m - 1.0 m = 29.0m

Figure 2.8.3 :

Flue Condensate Drain
Point Example

2.8.3 Slope

'Horizontal' flue outlet pipework
MUST slope at least 2 degrees (32
mm per metre run) downwards
towards the boiler where 100 mm
Keston Composite pipe is used.
Pipework can be vertical. Only
swept elbows can be used.
Air inlet pipework can be truly
horizontal or vertical, or sloping in a
downward direction towards the
boiler but in this case rain, etc.,
must be prevented from entering
the pipe. There must be no

troughs in any of the pipework, whether it be air inlet or flue outlet.

Due the low temperature of the flue gases further condensate will form within the
flue system. Drain points, with suitable traps, must therefore be incorporated
within the flue system at the base of vertical flue sections in excess of 8m, for
100mm Keston Composite pipe flue systems. These additional condensate drains
must be run to discharge as detailed in section 2.11. Such drain points can be
formed using standard plastic fittings. Refer to the example in Figure 2.8.3.

2.8.4 Terminations

Air inlet terminals must be facing horizontally or downwards to prevent entry of
rain into the terminal and positioned to ensure only fresh air is drawn into the
boiler. The air terminal must be located outside of the building.

To Terminal

To Boiler

Tee Fitting

6 in min.

Drawing of combustion air directly from a ventilated boiler room invalidates the
heat exchanger warranty.

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The flue outlet terminal is designed to face outwards but can, if desired, be
adapted to face in any direction BUT must not be directed in the region of the air
inlet. Where the air and flue terminals are located in close proximity, the flue
terminal should be located above the level of the air intake terminal
The two terminals are subject to the requirements of BS 5440 Pt 1 for clearances
from features of the building although some can be decreased to the values
indicated.

Dimensions (mm)

Flue

Terminal

Air

Inlet

etc.

lines

terminal

Table 2.8.4 Minimum Flue Terminations & Air Inlet Dimensions

50500A Below or beside openable window, air brick,

7575B Below gutters, soil pipes, drain pipes.

50300C Below eaves (unventilated)

50200D Below balconies or car port roof.

5075E From vertical drain or soil pipes.

50600F From internal or external corner or boundary

100300G Above ground or balcony or roof.

100600H From surface or boundary line facing a

1,2001,200I From terminal facing a terminal.

1001,200J From opening in a car port.

1,5001,500K Vertically from terminal on same wall.

300300L Horizontally from terminal on same wall.

The Keston C90 and C110, as with any condensing boiler, will generate a
condensate “plume” from the flue terminal in all weather conditions.
Consideration must therefore be given to the effect of this “plume” when
selecting a location for the flue terminal.

It is advisable for horizontal flue terminals to place a 45o elbow at the end of the
flue to direct the condensate plume up and away from the property.

2.8.5 Clearances From Wall

Flue outlet and air inlet terminations must be at least 40 mm from the wall face.

2.8.6 Distance Between Flue Outlet & Air Inlet

There is no maximum - the terminations must not be on opposite sides of the
dwelling but can be in areas of unequal pressure
A minimum clearance of at least 500mm must be left between the terminations
and the flue terminal must be directed away from the air intake terminal.

2.8.7 General Installations

All parts of the system must be constructed in accordance with BS 5440 Part 1,
except where specifically mentioned in these instructions.
All pipe work must be adequately supported.
All joints other than push-on or plastic compression connectors must be made
and sealed with solvent cement suitable for Keston Composite pipes and
conforming to BS 6209: 1982.
External wall faces and any internal faces of cavity walls must be made good.

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2.9 AIR SUPPLY

The C90 and C110 are room sealed appliances and therefore do not require purpose
provided ventilation to the boiler room for combustion air.

2.10 COMPARTMENT INSTALLATION

The C90 and C110 models operate with very low heat emission levels. As a results the
boilers can be installed in a compartment without ventilation for cooling purposes.

2.11 CONDENSATE DRAINAGE

Being a condensing boiler, the C90 and C110 are fitted with a condensate trap at the base
of the heat exchanger and flue assembly, with facility to connect to a drain point
underneath the appliance.

The connection to the boiler condensate outlet and the condensate discharge pipe work
within the dwelling must be sealed.

Use only plastic piping and do not reduce below 22 mm internal diameter within the
dwelling. Condensate should preferably be drained into the sanitary waste system or,
alternatively, the rainwater system of the property in most cases. Ensure in all cases that
the disposal of the condensate is in accordance with any local regulations in force.

Termination of the pipe must be either at a branch or stack internal to the house, or
externally at an open gully. Alternatively, discharge into a purpose made condensate
soakaway can be considered. Existing or purpose built drains must use suitable corrosion
resistant material as condensate is mildly acidic.

A minimum slope downwards towards the drain of 1 in 20 is essential. Freezing of the
termination and pipework must be prevented. Any drainage pipes outside the property
must be at least 32 mm inside diameter.

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3. INSTALLATION OF THE BOILER

Read Chapter 2 - Boiler Location and decide upon the position of the boiler.
Installation of the boiler is straightforward but consideration must be given to access to allow flue
and air pipes to be pushed through walls and ceilings. The order in which the components are
installed will depend upon particular site conditions, but in general it will be easiest and most
accurate to install the boiler and then build up the flue outlet and air inlet pipes to the terminal - this
is the sequence described.

3.1 WALL MOUNTING BRACKET

a. Place the bracket on the wall

horizontally with the pre-drilled
holes at the bottom.

b. Drill through the centre hole of

the brackets, plug the hole and
fix in position.

c. Using a spirit level make sure

the brackets are completely
level individually and relative to
each other and mark the
position of the other screw
holes.

d. Remove the bracket and drill the

holes in the positions marked.
Plug these holes.

e. Screw the bracket to the wall

using screws of an appropriate
size for the wall type (No. 12 x 2
inch wood screws normally
suffice).

3.2 MOUNTING THE BOILER - CAUTION MULTI-PERSON LIFT

a Using the detachable side lift handles supplied or via winch, lift and locate the

upper rear lip on the boiler to the boiler wall bracket.

b Move the boiler sideways to centralise the boiler on the bracket.

300

Figure 3.1 Wall Mounting Fixing Locations

All dimensions in mm.

3.3 FLOOR STANDING FRAME - OPTIONAL (Part No C.34.0.06.00.0)

If the optional floor standing frame is selected the frame should first be assemble and
secured firmly to the plant room floor. Suitable assembly instructions are included with the
floor standing frame pack.

Lift the boiler and lower into position onto the frame.

3.4 ASSEMBLY PRACTICE

Remove all plastic debris and burrs when installing air intake piping. Plastic filings caused
by cutting Keston Composite plastic pipe must not be allowed to be drawn into the
combustion air blower. Prevent dust entering the air intake when cutting on building sites.
Blower failure which is determined to be caused by plastic filings or other debris will not be
covered by guarantee.

3.5 INSTALLING FLUE AND AIR PIPES

When installing a replacement boiler, a new flue system must be fitted. DO NOT
RE-USE THE ORIGINAL FLUE SYSTEM.

Remember the flue pipe must slope downwards back towards the boiler and this is best
achieved using 92.5o bends.
a. From the two connections on the boiler, mark the positions of the two holes for

the flue and air pipes on the wall(s) or ceiling. To allow access to drill the holes it
may be necessary to temporarily remove the boiler. If the boiler stays put then it is
imperative that the front doors are closed and the two plastic pipes capped off

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whilst drilling. Under no circumstances must debris from the wall or cut pipes be
allowed to enter the appliance or the plastic pipework.

b. Drill the two holes in the wall/ceiling, preferably using a core drill.

c. Always thoroughly deburr all pipes and, most important, remove shavings from

within the pipe.

d. Assemble the pipework from the boiler connections to the exit from the first

wall/ceiling (remount the boiler if removed). When pushing pipe through walls,
ensure grit and dust is not allowed to enter the pipe.

ENSURE PIPES ARE FULLY ENGAGED INTO SOCKETS.

Connect the condensate drainage system and fill the condensate trap by pouring
water down the boiler flue spigot ( See Section 3.6 Condensate Drainage).

Make the final connection of flue and air pipe to the boiler using push on
plastic couplings. Ensure that the connectors are set vertically otherwise

leakage of condensate may occur which will corrode the casing. Do not use
adhesive on the 'push on' end of connecting couplings.

e. Using the same methods drill any further holes (always covering existing

pipework), cut and assemble the pipework.

f. From outside, complete the two terminations - See Section 2.8 Flue System and

make good all holes.

g. Support any pipes whose route could be displaced either of its own accord or by

accident. Any horizontal run over 1m or vertical runs of any length must always be
supported. Brackets should be placed at intervals of approximately 1m.

h. Check all connections for security.

3.6 CONDENSATE DRAINAGE

Connect the condensate drainage system to the boiler. It is advisable to use a detachable
fitting at connection to the boiler to enable easy removal for servicing.

Fill the condensate trap by pouring water into the boiler flue spigot until water is
seen to flow freely from the condensate drainage system. Make the final connection
of flue pipe to the boiler.

Details are provided in Chapter 2 - Section 2.11 Condensate Drainage
Connection : 22 mm plastic pipe.

3.7 WATER SYSTEM

Connect the flow and return pipework to the boiler. Details of system requirements are
given in Chapter 2 - Section 2.7 Water Systems.
Connections : 1.5" BSP F.

3.8 GAS SUPPLY

Connect the gas supply to the appliance. Details of gas supply requirements are given in
Chapter 2 - Section 2.6 Gas Supply. Supply of adequate gas pressure (with the boiler
running) is critical to ensure reliable operation of the boiler.
Connections : 1 inch BSP F.

3.9 ELECTRICAL SUPPLY

The entry point(s) for the electrical supply cable(s) is in the base of the appliance (see
Section 2.2 Service Connections fig. 2.1.2) via three cord grip bushes. Feed the cable(s)
through its bush and route inside the cabinet to the connection strip located to the front
top left of the cabinet.

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1. The electrical supply must be as specified in Chapter 2 - Section 2.4 Electrical.
WARNING : THIS APPLIANCE MUST BE EARTHED

2. All external controls and wiring must be suitable for mains voltage. Supply wiring
should be in PVC insulated cable not less than 1.0mm2 to BS 6500 Table 16
(material code H05VV-F).

3. The permanent live supply connection may be via a 5 amp fused double pole
switch, serving only the boiler. (Refer to Chapter 2 - Section 2.4 Electrical Supply).

4. Securely tighten the terminal screws and route the cable through the re-openable
cable clips. Ensure all cables are secured and that the cord grip bush is tightened
to securely grip the main cable at entry to the cabinet.
The supply cable(s) must be connected to the main terminals as follows:-

Terminal N - Blue wire (Neutral) for 5A permanent supply
Terminal L - Brown wire (Live) 5A permanent supply
Terminal E - Yellow/Green Wire (Earth)

Terminal SL1 - 230V Demand Signal from main zone
Terminal SL2 - 230C Demand Signal from DHW/Zone 2

Terminals 1,2,3,4 Optional Keston C90/C110 Outside Temperature

Sensor. This will activate weather compensated flow
setpoint when responding to a demand signal on
SL1

Ensure connection is made such that if the cable slips in its anchorage the current
carrying conductors become taut before the earthing conductor.

3.10 EXCHANGING A BOILER

Before removing an existing boiler add Fernox Supafloc , or equivalent cleaning agent, in
accordance with the manufacturers instructions. Open all radiator valves and fire the
boiler. When the system is fully heated, shut off the gas supply and drain down the central
heating system.

Important
The Keston condensing boiler contains components which could be damaged or blocked
by grease, dirt or solder etc. It is essential that sludge or scale is removed from an existing
system.
The guarantee provided with the Keston does not cover damage caused by system debris
or sludge.

Connect the new boiler as instructed in this manual and fit in accordance with Sections

3.1 to 3.9

For sealed systems, fill to a pressure of about 2.7 bar. Check the complete system for
water soundness. If leaks need to be rectified using flux or solder the system must be
flushed cold again before proceeding.

Reduce the pressure to the Initial System Design Pressure for sealed systems, if
applicable. Vent the system.

Gas Supply

The complete gas installation up to the boiler service cock must be checked for
soundness. BS 6891.

Electrical Installation

Carry out preliminary electrical safety checks, i.e. Earth continuity, Polarity, Resistance to
Earth, Short Circuit using a suitable test meter.

Initial Firing
The gas pressure setting is factory adjusted to within the required range and
should not normally need re-adjustment. If the reading is incorrect then check such

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factors as soundness of the air and flue pipe joints, pressure sensible joints and the gas
inlet pressure (20 mbar required). If all joints are sound and the gas inlet pressure is
satisfactory set the gas pressure. Full details of this procedure are given in Section 4.7
Checking The Gas Pressure. This will ensure that combustion is good enough to allow
combustion fine tuning to take place.

Combustion Fine Tuning

It is advisable on all installations that the combustion quality is checked by measuring the
carbon dioxide (CO2), or oxygen (O2), level. This procedure is detailed in Section 4.6
Combustion Testing. Badly tuned combustion will lead to reduce the life of the boiler and
invalidate the warranty.

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20

4. COMMISSIONING OF THE BOILER

Important:
This condensing boiler contains components which could be damaged or blocked by grease, dirt, solder etc.,

from the water system. The following commissioning procedures must be followed precisely.

4.1 INITIAL FLUSHING

All waterways within the Keston C90 and C110 are either copper, high alloy stainless steel or aluminium. As a

result water treatment chemicals for central heating boilers such as Fernox MB1, Sentinel X100 or
equivalent, are suitable. In any event reference must be made to BS 7593 : Treatment Of Water In Hot
Water Central Heating Systems.

a. Disconnect the boiler from the system at the flow and return connections and temporarily link the flow

and return pipes on the system.

b. Flush the entire system until clean water is discharged, free from dirt, flux, solder etc. The use of a

flushing chemical is recommended, e.g. Fernox Supafloc, or equivalent.
Sludge and scale must be removed from an existing system. Boiler failure due to system debris or

sludge shall invalidate the guarantee.

c. Connect the system to the boiler and fill in accordance with Section 2.7 - Water Systems. At this stage,

for sealed systems, fill to a pressure of about 2.7 bar.

d. Check the complete system for water soundness. If leaks need to be rectified using flux and solder, the

system must be flushed cold again before proceeding.

e. Reduce the pressure to the Initial System Design Pressure for sealed systems, if applicable. Vent the

system.

4.2 GAS SUPPLY

The complete gas installation up to the boiler service cock must be checked for soundness. BS 6891.

4.3 ELECTRICAL INSTALLATION

Carry out preliminary electrical safety checks, i.e. Earth continuity, Polarity, Resistance to Earth, Short
Circuit using a suitable test meter.

4.4 INITIAL FIRING

Important
Checking the gas pressure to the pre-mix burner requires a special procedure, outlined below, which

must be carried out.
a. Purge the gas supply in accordance with BS 6891.
b. Vent the water system.

Important:

The heat exchangers consist of crossflow tubes which can trap an air pocket. Great care must be
taken to ensure that water flow has been established through the heat exchangers and thus ensuring
no air pockets remain in the heat exchanger and pipe work. Firing the boiler while an air pocket exists

in a heat exchanger could damage it.
c. Turn both the integral the gas service cocks to ON.
d. Turn on the electrical supply, setting the main zone (SL1) external controls to call for heat.

e. Adjust the upper rotary control knob, central heating temperature, to the maximum clockwise position.

Once a demand is received the left hand digit of each of the boiler module displays will change to “1” to

indicate each burner has entered the 10 second pre-purge phase. During this phase the module fan

and pump will start to run. The digits will then change to “2” to indicate ignition is taking place whilst the

gas valve are opened and the spark generated. Once the gas has ignited at the main burners the left

hand digits will change to “3” to show the relevant burner is alight.

If an air lock or other blockage is present a module may go to overheat or water pressure lockout. This

will be indicated by the first digit of the module display showing “9” and a flashing error code starting

with “b”. If this occurs clear the blockage and/or purge the air from the system, and press the module

“Reset” button to restart the ignition sequence. If ignition does not occur on a module, the module, at

approximately 20 second intervals, will make four further attempts to light the burner.

If after five automatic attempts the module still fails to ignite, the display will show the code “E 02”

indicating no ignition.

If, after five manual attempts (to allow for purging of any air in the gas line), the boiler still fails to ignite

(indicated by the error code “E 02”) refer to Section 5.3 - Fault Modes.
f. If the DHW/Zone 2 feature is used this should also be tested. Set the DHW/Zone 2 control to call for

heat and adjust the lower rotary control knob, DHW/Zone 2 temperature, to the maximum clockwise

position. Rotate the upper rotary control knob to the maximum anticlockwise position.

Once the DHW/Zone 2 demand is received the integral diverter valve will divert module 1 flow output to

the DHW flow connection. Once in position, the left hand digit of the left hand module will change to “1”

to indicate the burner has entered the 10 second pre-purge phase. During this phase the left hand

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21

module fan and pump will start to run. The digits will then change to “2” to indicate ignition is taking
place whilst the gas valve is opened and the spark generated. Once the gas has ignited the left hand
digit will change to “4” to show the left hand module is alight and serving DHW/Zone 2 demand.

g. Check for gas soundness between the each gas service cock and connection to the burner

manifold.

4.5 HOT FLUSHING

a. Allow the system to heat up, checking for water soundness.
b. Follow instructions provided with the cleaning agent, i.e. Fernox Supafloc, or equivalent. Turn off the

boiler and flush the water system while still hot. Thoroughly flush the system with clear water.

c. Refill the system using a quality water treatment such as Fernox MB1 or Sentinel X100. For sealed

systems, fill to the required Initial Design Pressure.

4.6 COMBUSTION TESTING

Although the gas pressure is preset at the factory it is required to assure proper combustion by
measuring gas input and the level of carbon dioxide, or oxygen and carbon monoxide, in the flue outlet
from the boiler. Over firing or under firing the burner will reduce the longevity of the appliance and may

result in excessive carbon monoxide levels.
Carbon dioxide and carbon monoxide are colourless, odourless gases produced by all combustion
processes. When the Keston condensing boiler is operating properly, carbon dioxide (CO2) levels will be
between 8 & 8.2% (C90 low rate), 8.3 & 8.5% (C110 low rate), 8.2 & 8.7% (C90 high rate) and 8.6 & 9%
(C110 high rate) and carbon oxide (CO) levels will be between 5 to 20 ppm (low rate) and 50 to 150 ppm
(high rate) for natural gas. In any event, the CO2 level at low rate must ALWAYS be less than CO
levels at high rate.
To measure CO2 levels in the Keston boiler remove the 1/8" plug from the flue outlet pipe spigot (Figure

5.7.2 1/2 item 97). Insert the probe of a calibrated combustion analysis meter and sample the gases as
instructed in the test equipment's instructions.
When firing the boiler for the first time since installation, the CO level at high rate may be between
100-220 ppm and between 50-80 ppm at low rate. This is due to compounds used during manufacture
curing within the combustion chamber. On boilers which have been fired for more than one hour since
installation, the CO levels should not exceed 150 ppm at high rate and 50 ppm at low rate. If CO levels
above these values are experienced, the combustion chamber and flue system should be investigated.
The C110 & C90 are factory set for combustion and should need no adjustment. However, in the event
adjustment is required.
Check combustion errors are not a result of incorrectly installed flue and/or air system, terminal location

or damage or debris on the burner. If all these factors are found to be in order precede as follows:

1) Set any controls to call for heat.

2) Set the boiler to run at maximum / minimum fan speed. To do this is necessary to access the
hidden buttons (behind the “KESTON” label under the display). There are five buttons, which are used to
adjust settings and provide additional boiler information. The drawing below shows the layout of these
buttons and their function.

To set the fan to maximum
Press the “Mode” button repeatedly until the display shows

“Stby”.

Press and hold the “Mode” and “+” key together for 2 seconds.
The display will then show “H nn”. The unit is now locked on
max fan speed

3) Measure the CO2 reading in the flue gases and adjust,

if necessary, the adjustment screw (pos. 5) to produce a CO

2

reading of 8.2% to 8.7% for C90 and 8.6% to 9% for C110 with

a corresponding CO level of 50 to 150 ppm for natural gas.

NORMAL ADJUSTMENT, IF REQUIRED, SHOULD NEED NO

MORE THAN HALF OF ONE ROTATION OF THE

ADJUSTMENT SCREW (pos. 5).

To set the fan to minimum

Press the “Mode” button repeatedly until the display shows

“Stby”

Press and hold the “Mode” and “-“ keys together for 2 seconds. The display will

then show “L nn”. The unit is now locked on min fan speed.

4) Measure the CO2 reading in the flue gases. The CO2 reading must be 8% to 8.2% for C90 and

8.3% to 8.5% for C110 with a corresponding CO level of 5 to 20 ppm for natural gas. THE CO2 LEVEL

AT LOW RATE MUST ALWAYS BE LESS THAN THE CO2 LEVEL AT HIGH RATE.

2

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Installation & Servicing Instructions

Page :

22

If following the above procedure, combustion levels described above at both high and low rate
could not be obtained, please turn off the appliance and isolate the gas to the appliance.

Telephone KESTON BOILERS technical support (phone no. 0208 462 0262)

To revert to normal modulation
Press the “Mode” button repeatedly until the display shows “Stby”
Press and hold the “+” and “-“ keys together for 2 seconds.

This process should be repeated for each module operating individually and together.

4.7 CHECKING THE GAS PRESSURE

NB: It is advisable to carry out this test with the user control knob turned to maximum and the
system water cold to ensure the boiler is running at maximum rate.
The gas setting is factory adjusted to within the
required range and should not need adjustment. If the
reading is incorrect then check such factors as
soundness of the air and flue pipe joints and the gas
inlet pressure (pos. 3) (minimum 18 mbar required for
natural gas). If all joints are sound and the gas

inlet pressure is satisfactory check the gas input
by timing the gas meter as detail in Section 4.8

Timing The Gas Meter. If the gas input cannot be
measured then it’s compulsory to measure the
combustion quality as detail in Section 4.6
Combustion Testing.

4.8 TIMING THE GAS METER

After the boiler has been started, and with no other appliances using gas, time the gas meter to be
certain that the unit is running at the proper gas input. Determine the cubic feet of gas passing through the
meter and determine the input in Btu per hour. Input must be within plus or minus 5% of the rated input.

Time, in seconds, the time taken to pass 2 cubic feet of gas through the meter (i.e. one revolution of a 2
cu ft dial) or 0.1 cubic metres if the meter is of the new metric digital type.

Model Time for 2 cu ft Time for 0.1 cu m

C90 (natural gas) 24 seconds 42 seconds

C110 (natural gas) 19 seconds 34 seconds

If the meter timing is found to be incorrect when both the boiler modules are firing at maximum rate

contact Keston Boilers Ltd for further guidance

4.9 HANDING OVER TO THE USER

It is important to fully explain the following:
a. Procedure to light and turn off the boiler, including isolation of the electrical supply if necessary.
b. The function of the lockout feature must be explained :

If the display shows “E 02” this means that that module has failed to light. Press the “Reset” button and
wait.
i) If lockout recurs immediately then the gas supply should be checked as ON, otherwise consult a
Service Engineer.
ii) If it is not possible to relight, the boiler must be isolated and a Service Engineer called in to
rectify the fault.

c. Advise that a reduction in the water pressure reading on the system pressure gauge, for sealed

systems, indicates a leak which should be rectified before further use.
d. Advise that the appliance should be serviced by a competent person at least once a year.
e. Advise on the frost protection and pump/fan exercise feature.
f. Hand over User Instructions.
g. Advise the user that a plume of water vapour (steam) from the flue terminal is normal and that there is

no need for concern.

WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5. FAULT FINDING

5.1 ELECTRICAL CONTROL SEQUENCE

The C90 and C110 feature digital displays to detail the operating status of each of the two
modules contained in the boiler. When serving a demand signal on SL1 only both displays
will show very similar temperatures (the last two digits) and matching status, allowing for a
small delay between operation of each module.
In the event a demand signal is received on SL2 (i.e. DHW demand) the left hand module is
“seconded” away from serving the main zone flow and will operate independently of the right
hand module to serve the DHW demand at the temperature specified using the lower rotary
knob. The output of the left hand module is diverted to the DHW Flow output connection by
an integral diverter valve. Once the demand signal on SL2 is removed, the left hand module
re-joins the right hand module to resume serving the demand from the main zone
In this way the boiler is able to produce two different flow temperatures at the same time.

When the external controls are calling for heat, power will be fed to the boiler connection
strip at terminals SL1 (Switched Live 1) &/or SL2 (Switched Live 2) and N (Neutral). If the
user control setting on the relevant knob is to a temperature less than the boiler flow
temperature the relevant module display will show “6 nn” where nn is the actual boiler flow
temperature. If the user control setting of the relevant knob is to a temperature above the
actual boiler flow temperature and provided all temperature thermostats and pressure
switches are closed the module control PCB will initiate the following sequence for the
relevant module.

(1) The fan will start.
(2) When the fan reaches running speed, the control PCB will start the ignition

sequence and the first digit of the display will show “1”.

(3) After a pre-purge period of about 10 seconds, the first digit of the display will show

“2”, the gas valve will open to allow gas to mix with the air at the suction side of the
fan and the ignition spark will occur at the main burner.

(4) When the burner ignites, the flame is detected by the control PCB through the

combined flame sensor/ignitor and the ignition spark is stopped. The first digit of the
display will show “3” or “4” depending on the external demand being served. The
module is now in its normal run condition.

(5) The module will automatically and continuously adjust its power output and pump

speed to best match the demands of the system at any time.

(6) The burner will continue to operate until the gas valve interrupts the gas supply. The

gas valve will be closed by the control PCB if power is interrupted to the boiler by
any external control or the boiler thermostat. If an interruption to the gas supply
causes loss of the flame, the control box will pause for approximately 10 seconds
and then attempt to re-ignite the unit. If this attempt fails, i.e. due to continued lack
of gas supply, the boiler will make four further attempts to ignite at intervals of
approximately 10 seconds and will then go to a lockout state (the display shows “E
02”). Once the gas supply has been resumed the boiler can be reset by pressing
the “Reset” button.

(7) The boiler can also be shut down by the cabinet temperature sensor or flue

overheat thermostat.

Any failure of the boiler to sequence in the above manner should be investigated using the
following trouble shooting flow diagram.

Before attempting any electrical fault finding, always carry out preliminary electrical system
checks. On completion of any service/fault finding task which has required the breaking and
remaking of electrical connections, the checks, earth continuity, polarity, short circuit,
resistance to earth must be repeated.

QUICK REFERENCE

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.2 NORMAL OPERATION

The C90 and C110 boilers feature a user display
which shows actual flow temperature of each
module at all times (the last two digits of the
display) and a status number (the first digit) which
identifies what the module is doing at any given
time. The table below shows the range of status
codes which will be displayed as part of normal
module operation:

NORMAL OPERATION CODES

MeaningDisplay

0 nn

1 nn

2 nn

3 nn

4 nn

5 nn

6 nn

7 nn

8 nn

A nn

Boiler in standby waiting for

demand signal

Boiler is running fan prior to

attempting ignition
Boiler has opened gas valve and is
sparking at ignitor
Boiler is alight and running in

response to a demand

from central heating (i.e.

SL1)
Boiler is alight and running in

response to a demand

from DHW (i.e. SL2)
Temporary mode whilst boiler is

adjusting internal settings
Burner is off because the boiler is

up to temperature
Boiler pump is in Central Heating

overrun mode (2 mins)
Boiler pump is in DHW overrun

mode (2 mins)
Temporary mode whilst boiler is
adjusting internal settings

5.3 FAULT MODES

5.3.1 Automatic Lockout Avoidance

The module will react to adverse conditions in two ways. If the fault is not severe, or is not
persistent, the module will halt (or block) operation for a set time before it attempts to fire again.
During this block time the block code will be displayed, alternately with the code “9 nn”, where nn
is the module flow temperature.

BLOCK CODES

Reason for blockDisplay

Flow temperature exceed 95oCB 18
Return temperature exceeded 95oCB 19

B 24

Installation & Servicing Instructions Page : 24

Return temperature exceeded flow temperature. Check pump direction on boiler
and any external pumps. Check wires on flow and return thermistors are not
crossed.
Flow temperature climbing too quickly. Possible air lock or circulation blockageB 25
Low water pressureB 26

WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

No signal from fan. Possible fan disconnected or faulty.B 28
Incorrect signal from fan. Possible fan faulty.B 29
Difference between flow and return temperatures too high. Check water circulationB 30
Waiting for fan to startB 65

5.3.2 LOCKOUT

If the fault is persistent or more severe the module will lockout with a error code. When the module
has entered this error mode it will not attempt to restart until the “Reset” button is pressed.

ERROR CODES

Description of faultDisplay

Flame detected when not expected. Check boiler earth and probe condition.E 00

E 02

No ignition after restart. Check gas supply, gas valve operation and ignitor electrode
spark generation.
Gas valve faulty or not connectedE 03
Power has been reset whilst boiler was in lockoutE 04
Internal electronics error - rest or replace control boxE 11
Thermal fuse blown or flue overheat thermostat activated.E 12
Flow overheat - check water circulationE 18
Maximum return temperature exceeded. Check circulation.E 19
Flow temperature increased too quickly. Check water circulation.E 25
Fan not rotating - check fan connection and fan for fault.E 28
Difference between flow and return temperatures too high. Check circulation.E 30
Flow thermistor short circuit - check/replace connections/thermistorE 31
Return thermistor short circuit - check/replace connections/thermistorE 32
Flow thermistor open circuit - check/replace connections/thermistorE 36
Return thermistor open circuit - check/replace connections/thermistorE 37
Low water pressureE 44

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.4 FUNCTIONAL FLOW WIRING DIAGRAM

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.5 ELECTRICAL WIRING DIAGRAM

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.6 ILLUSTRATED WIRING DIAGRAM

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.7 Exploded Assembly Diagrams

5.7.1 Boiler Controls Assembly

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.7.2 Waterway, Condensate & Flue Assembly.

5.7.3 Air - Gas Assembly

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.7.4 Casing Assembly

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

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WD352/0/2003 Chapter 5 : Fault Finding The Keston C90 & C110

5.7.5 Exploded Diagrams Parts Reference List

Boiler Controls Assembly (Fig. 5.7.1)
GC Number Code Description

E93-126 134 Main Control Box

(C.17.4.01.00.0)

E93-130 147 Control Panel (C.17.4.02.00.0)

- 161 Terminal Block 2 (C.17.4.06.00.0)
E72-401 138 Thermal Fuse (C.08.4.21.00.0)
E93-135 146 Ignitor Cable (C.17.4.07.00.0)

Waterway, Condensate & Flue Assembly (Fig. 5.7.2)
GC Number Code Description

E93-136 48 Heat Exchanger (C.17.2.02.00.0)
E93-137 44 C110 Burner (C.17.2.01.00.1)
E93-138 44 C90 Burner (C.13.2.01.00.0)

E93-141 56 Burner Head Gasket (C.17.2.00.09.0)
E93-142 55 Ignitor Gasket (C.17.2.00.62.0 A)
E93-143 42 Spark Ignition Electrode

(C.17.2.29.00.0 A)

- 76 Condensate Trap (C.34.2.03.00.0)
E93-145 67 Flow/Return Thermistor (C.17.2.04.00.0)
E72-332 66 Flue Overheat Stat (C.08.2.30.00.0)
114-045 68 Water Pressure Switch (B.04.2.23.00.0)
E93-146 72 Water Pump (C.17.2.06.00.0)
E73-355 97 Combustion Test Plug (B.04.2.00.49.1)

Air - Gas Assembly (Fig. 5.7.3)
GC Number Code Description

E93-147 114 Combustion Blower (C.17.3.01.00.0 A)

193 Gas Valve - Mixer Air-Gas

Assembly (C.17.3.17.00.0)

Casing Assembly (Fig. 5.7.4)
GC Number Code Description

- 10 Cabinet Door (C.34.1.02.00.0)

- 8 C110 Databadge (C.34.1.00.01.0)

- 8 C90 Databadge (C.26.1.00.01.0)

Installation & Servicing Instructions Page : 33

WD352/0/2003 Chapter 6 : Servicing The Keston C90 & C110

6. ROUTINE (ANNUAL) SERVICING

To ensure the continued safe and efficient operation of the boiler it is necessary to carry out
routine servicing at regular intervals. The frequency of the servicing will depend upon the particular
operating conditions, but it is recommended that an annual service should be carried out by a
qualified engineer.

It is the law that any service work must be carried out by competent qualified persons.

NB: When servicing ensure that the gas and electrical supplies to the boiler are isolated before

any work starts. It should be noted that setting the user controls to “Standby” does not
isolate the electrical supply and parts of the boiler will remain live.

Hazardous materials are not used in the construction of the C90 and C110. However, due care
should be taken when handling boiler components.
All joints should be checked for soundness after servicing and before firing the appliance.

6.1 Pre-Service Checks

It is recommended that an inspection should be carried out prior to shutting down the unit
for servicing. Remove the front door by removing the screws retaining the top and lifting
the front panel clear of the bottom. The following items should be observed:

a. Smooth starting and running of each module blower.
b. Smooth lighting of each burner.
c. Check for leakage of gas, gas/air or combustion products.
d. Check for condensate leaks.
e. Check that the modules do not enter “blocks” in operation whilst running

(indicated by the display alternating between “9 nn” and “B nn”, where nn
indicated either the flow temperature or the block code). If so refer to section 5.2

and section 5.3 for details of code meanings and rectify.
f. Check for water soundness.
g. Inspect the flue vent and air intake pipework. Joints must be sound and all

pipework well bracketed.
h. Check that there is a steady fall back to the boiler from the flue pipe to allow

condensate to run back into the boiler.
i. With the boiler operating at a low return temperature (i.e. less than 50oC) check

that the condensate flows freely from the condensate line.

6.2 Recommended Routine Module Service

a. Remove the outer case by first removing the securing screws at the front of the

appliance.
b. Remove the burner head (Section 7.6) and inspect the burner appearance (both

heat exchangers). Black markings or other discoloration's on the gauze indicate

too much gas or a lack of air possibly due to a blocked air inlet. Any breakage's or

damage to the burner mesh indicate the burner must be replaced.
c. If necessary clean the burner with a mild household detergent and rinse under a

hot running tap.
d. If necessary, from visual inspection, clean the heat exchanger using a suitable

stiff plastic bristle brush, vacuum out any large particles and flush the heat

exchanger with fresh water until the water flowing from the condensate drain is

clear.
e. Remove the condensate trap (Section 7.8) and clean by flushing through with

clean running water.
f. Check the electrode assembly mounted on the heat exchanger. If the point is

damaged or burnt replace it.

Check that the spark gap measures 3 mm.

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WD352/0/2003 Chapter 6 : Servicing The Keston C90 & C110

g. Replace the burner head, renewing the gasket if necessary, and reconnect the

gas/air supply. Ensure the flanged gas/air supply joint is air tight.

h. Turn on the electrical supply to the boiler and allow the boiler to reach operating

temperature levels.

i. Remove the combustion test point plug from the flue pipe. This is situated on the

flue spigot out of the cabinet.

j. Carry the full procedure detailed in section 4.6 COMBUSTION TESTING -

MANDATORY

k. Replace the combustion test point plug.
l. Recheck the burner pressure by following the procedure detailed in Section 4.7.

m. Check all joints for soundness up to the gas burner.
n. Repeat the procedure for the other module

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WD352/0/2003 Chapter 7 : Replacement Of Parts The Keston C90 & C110

7. REPLACEMENT OF PARTS

CONTENTS

7.0 GENERAL

7.1 PRECAUTIONS

7.2 ACCESS

7.3 REPLACEMENT PROCEDURE

7.4 ELECTRICAL COMPONENTS

7.4.1 CONTROL PANEL

7.4.2 MODULE FLOW & RETURN THERMISTORS

7.4.3 CABINET TEMPERATURE SENSOR

7.4.4 FLUE PROTECTION THERMOSTAT

7.4.5 WATER PRESSURE SWITCH

7.4.6 MAIN CONTROL BOX

7.4.7 COMBUSTION BLOW ER

7.4.8 GAS CONTROL VALVE / VENTURI ASSEMBLY

7.5 SPARK IGNITION/FLAME DETECTION ELECTRODE

7.6 BURNER

7.7 HEAT EXCHANGER

7.8 CONDENSATE TRAP

7.9 PUMP

7.0 GENERAL

The following must always be carried out by a competent/qualified person.

7.1 PRECAUTIONS

i) Always switch off the mains electricity supply and disconnect the plug at the

isolating switch and socket. (If a switch only is used then remove the fuse.)
ii) Gain access to the appliance (Section 7.2) and turn off the gas supply at the

appliance service cock.

WARNING : Parts of the boiler internal wiring will remain live even after setting

the User Controls to Standby. Shut off the power supply at the
isolating switch before working on the appliance.

7.2 ACCESS

i) Remove the cabinet door by removing the screws from the front of the cabinet.

7.3 REPLACEMENT PROCEDURE

i) Always replace in the reverse order unless otherwise stated.
ii) Electrical connections must be remade in accordance with the Electrical Wiring

Diagram (Section 5.5).
iii) Test the soundness of any gas carrying or water carrying joint broken during the

service procedures.

7.4 ELECTRICAL COMPONENTS

7.4.1 Control Panel (Fig. 5.7.1 item 135)

i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)

iii) Remove the user control cover by removing the four retaining screws (Fig

5.7.1, item 136).

iv) Disconnect the Control Panel by unplugging the ribbon cable connection

block.

v) Disconnect the potentiometers (Fig 5.7.1, item 149) by unplugging the

cable connection.
vi) Reassemble (Section 7.3)
vii) Check for correct operation of the Control Panel.

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WD352/0/2002 Chapter 7 : Replacement Of Parts The Keston C90 & C110

7.4.2 Module Flow and Return Thermistors (Fig. 5.7.2 item 67)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the push on connectors from the thermistor taking note of the

correct positions.
iv) Unclip the thermistor from the pipe.
v) Reassemble (Section 7.3)

NB: When fitting the new thermistor it is an advantage to smear a thin

film of heat sink compound between the thermistor and pipe.
This, combined with fitting the new thermistor tightly to the pipe,
ensures a good contact.

7.4.3 Cabinet Temperature Sensor (Fig 5.7.1 item 138)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the cabinet temperature sensor from the connector block by

slackening the retaining screws.

iv) Reassemble (Section 7.3)

7.4.4 Flue Protection Thermostat (Fig. 5.7.2 item 66)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the push on connectors from the thermostat taking note of the

correct positions.
iv) Unscrew the two retaining screws, or nuts, and remove the thermostat.
v) Reassemble (Section 7.3)

NB: When fitting the new thermostat it is an advantage to smear a

thin film of heat sink compound between the thermostat and
plate. This, combined with fitting the new thermostat tightly to the

plate, ensures a good contact.

7.4.5 Water Pressure Switch (Fig. 5.7.2 item 68)
i) Isolate the appliance (Section 7.1)
ii) Shut off the water supply to the appliance.
iii) Gain access (Section 7.2)
iv) Drain the system to below the level of the appliance using the drain off

tap at the base of the return pipe from the heat exchanger.

v) Remove the push on connectors from the water pressure switch taking

note of the correct positions.
vi) Unscrew the pressure switch.
vii) Reassemble (Section 7.3).

NB: Use a little jointing compound or PTFE tape on the thread.
viii) Refill the system (See Section 4 - Commissioning).

7.4.6 Main Control Box (Fig. 5.7.1 item 134)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Pull off the multi-pin connectors and HT lead away from the board.
iv) Remove the three retaining screws securing the control block to the boiler

backframe.
v) Remove the control box.
vi) Reassemble (Section 7.3)

7.4.7 Combustion Blower (Fig. 5.7.3 item 114)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Disconnect the two connector blocks from the combustion blower.
iv) Unscrew the bolts securing the venturi (fig 5.7.3 item 120) to the inlet port

of the combustion blower.

v) Remove the four bolts securing the combustion blower (fig. 5.7.3 item

119) outlet flange to the burner and remove the combustion blower.

vi) Reassemble (Section 7.3)

NB: When reassembling inspect any gaskets for damage and replace

if necessary.

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WD352/0/2003 Chapter 7 : Replacement Of Parts The Keston C90 & C110

7.4.8 Gas Control Valve / Venturi Assembly (Fig. 5.7.3 item 193)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the push on connector block to the gas valve.
iv) Unscrew the bolts (Fig 5.7.3 item 127) securing the gas inlet pipe to the

gas control valve / venturi assembly.

v) Unscrew the bolts securing the gas control valve / venturi assembly (Fig

5.7.3 item 120) to the inlet port of the combustion blower.
vi) Remove the gas valve/venturi assembly as a complete unit.
vii) Reassemble (Section 7.3)
viii) Check the gas rate and combustion (See Section 4 - Commissioning)

NB: Always change the gas valve/venturi assembly together. This

assembly is factory preset but must be checked using the
procedure set out in Section 4.6 (Combustion testing).

7.5 SPARK IGNITION/FLAME DETECTION ELECTRODE (Fig. 5.7.2 item 42)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the pull off HT lead to the spark ignition electrode.
iv) Undo the screws to the spark ignition electrode flange located on the heat

exchanger side panel and withdraw the spark ignition electrode.

v) Reassemble (Section 7.3)

NB: When reassembling inspect the gasket for damage and replace if

necessary.
With the new spark ignition electrode in place it is essential to ensure the
gap between the tip of the electrode and the earth post is 3 mm.
Distances above or below 3 mm will affect ignition performance. If
necessary gently bend the electrode taking care not to damage the

ceramic insulator.

7.6 BURNER (Fig. 5.7.2 items 44)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the combustion blower (Section 7.4.7)
iv) Remove the 12 nuts fixing the burner to the top of the heat exchanger.
v) Withdraw the burner from the top of the heat exchanger.
vi) Reassemble (Section 7.3)

NB: When reassembling inspect any gaskets for damage and replace if

necessary.

7.7 HEAT EXCHANGER (Fig. 5.7.2 item 48)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Shut of the water supply to the appliance.
iv) Remove the burner (Section 7.6)
v) Drain the system to below the level of the appliance using the drain off tap at the

base of the boiler return pipe.
vi) Remove the flue protection thermostat (Section 7.4.4)
vii) Remove the spark ignition/flame detection electrode (Section 7.5)
viii) Remove the flue connection by slackening the retaining strap and pulling the flue

off the heat exchanger spigot.
ix) Remove the condensate trap hose (Fig 5.7.2 item 73 or 74) by releasing the

retaining clamp and pulling the hose away from the spigot at the base of the heat

exchanger flue outlet box.
x) Disconnect the flow pipe union (Fig.5.7.2 item 62) and the return pipe union

(Fig.5.7.2 item 57) from the heat exchanger.
xi) Remove the two screws fixing the heat exchanger to the top mounting bracket

(Fig 5.7.2 item 78)

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WD352/0/2002 Chapter 7 : Replacement Of Parts The Keston C90 & C110

xii) Remove the heat exchanger
xiii) Reassemble (Section 7.3)
xiv) Recommission (Section 4 - Commissioning)

7.8 CONDENSATE TRAP (Fig. 5.7.2 item 76)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Disconnect the condensate line from the base of the heat exchanger.
iv) Disconnect the condense line from the projection of the condensate trap from the

base of the cabinet.
v) Withdraw the condensate trap.
vi) Mop up any spilled condensate.
vii) Reassemble (Section 7.3)

NB: When re-fitting the condensate trap pour water onto the condensate hose

from the base of the heat exchanger until nearly full. Then reconnect the
condensate hose to the base of the heat exchanger.

7.9 PUMP (Fig 5.7.2 item 72)
i) Isolate the appliance (Section 7.1)
ii) Gain Access (section 7.2)
iii) Isolate the waterways to the pump using the pump isolation valves(Fig 5.7.2 item

71)

iv) Disconnect the pump electrical cable from the connections box of the pump head

taking note of the correct position.
v) Remove the four allen bolts securing the pump head to the pump back plate.
vi) Remove the pump head.
vii) Reassemble (Section 7.3)

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WD352/0/2003 Chapter 8 : Spare Parts Listings The Keston C90 & C110

8. SHORT SPARE PARTS LIST

Item GC No Part Denomination Item GC No Part Denomination

44 E93-137 C110 Burner 56 E93-141 Burner Gasket

E93-138 C90 Burner

55 E93-142 Ignitor Gasket 42 E93-143 Ignitor/Sensor Probe

67 E93-145 Flow/Return Thermistors 66 E72-332 Flue Thermostat

193 Gas Valve / Venturi Assembly 134 E93-126 Main Control Box

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WD352/0/2003 Chapter 8 : Spare Parts Listings The Keston C90 & C110

SHORT SPARE PARTS LIST FOR THE KESTON

CONDENSING BOILER RANGE

Item GC No Part Denomination

67 E93-145 Flow/Return Temperature Thermistor

68 114-045 Water Pressure Switch

66 E72-332 Flue Protection Thermostat

134 E93-126 Main Control Box

135 E93-130 Control Panel

114 E93-147 Combustion Blower

193 Gas Valve / Venturi Assembly

76 E93-144 Condensate Trap

42 E93-143 Ignition Electrode

44 E93-137 Burner (C110)

44 E93-138 Burner (C90))

48 E93-136 Heat Exchanger

72 E93-146 Circulating Pump

138 E72-401 Cabinet Temperature Sensor

Installation & Servicing Instructions Page : 41

KESTON CONDENSING BOILERS

IMPORTANT

C90 & C110

INSTALLATION KEY POINTS

†

†

†

†

†

†

†

†

Read Installation Manual Carefully

Ensure that there is at least 9 feet head of water pressure at the
top of the boiler .

Ensure that ALL dust particles, filings , plastic chips etc. are
removed from the inlet pipe.

If the installation is a replacement the system must be flushed
clean. System should be drained hot, then refilled, then drained

again until the water is clean.
Ensure that there is a proper electrical supply i.e. 230V fused at

5A for the permanent live.
Take great care with pipe connections to ensure that no

damage is done to the internal pipework.
Ensure that the 22mm condensate pipe is not exposed to

freezing conditions.
Make sure that the exhaust pipe terminates away from windows

or vents and is out of reach.

†

†

†

†

†

Make sure that the air inlet and exhaust pipe outlets are at least
500mm apart.

Check tightness of all connections in the boiler before firing.

Ensure that the terminals supplied are fitted to both the exhaust
and air inlet pipes.

The system must be free from air before firing.

Complete the combustion testing (Section 4.7) using a
calibrated flue gas analyser.

WD357/1/2008

WD483/0/2008

CCCC110

110 & C

110110

& C9

& C & C

90

99

0

00

Gas valve/Venturi assembly replacement procedure for

KESTON C110 and C90 boilers.

These conversion instructions must be read in conjunction with the Keston C110 & C90 Installation &
Servicing Instructions – WD352.

Before proceeding to the replacement procedure please check if the tamper paint on the offset adjustment cap
(see attached picture) is intact. If the tamper paint is broken please return the assembly to KESTON
BOILERS.
Do not dismantle the gas valve/venturi assembly. Always change the gas valve/venturi assembly together.

To replace the gas valve/venturi assembly you must carry out the following sequence:

1. Isolate the appliance (Section 7.1)

2. Gain access (Section 7.2)

3. Remove the push on connector block to the gas valve.

4. Unscrew the bolts (Fig 5.7.3 item 127) securing the gas inlet pipe to the gas control valve / venturi
assembly.

5. Unscrew the bolts securing the gas control valve / venturi assembly (Fig 5.7.3 item 120) to the inlet
port of the combustion blower.

6. Remove the gas valve/venturi assembly as a complete unit.

7. Reassemble (Section 7.3)

8. Check the gas rate and combustion – MANDATORY

Although the gas pressure is preset at the factory it is required to assure proper combustion by
measuring gas input and the level of carbon dioxide, or oxygen and carbon monoxide, in the flue
outlet from the boiler. Over firing or under firing the burner will reduce the longevity of the appliance
and may result in excessive carbon monoxide levels.

Carbon dioxide and carbon monoxide

are colourless, odourless gases
produced by all combustion processes.
When the Keston condensing boiler is
operating properly, carbon dioxide
(CO2) levels will be between 8 & 8.2%
(C90 low rate), 8.3 & 8.5% (C110 low
rate), 8.2 & 8.7% (C90 high rate) and

8.6 & 9% (C110 high rate) and carbon

oxide (CO) levels will be between 5 to
20 ppm (low rate) and 50 to 150 ppm
(high rate) for natural gas.

In any event, the CO2 level at low rate

must always be less than CO2 levels at
high rate.

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WD483/0/2008

To measure CO2 levels in the Keston boiler remove the 1/8" plug from the flue outlet pipe spigot

(Figure 5.7.2 1/2 item 97). Insert the probe of a calibrated combustion analysis meter and sample the
gases as instructed in the test equipment's instructions.

When firing the boiler for the first time since installation, the CO level at high rate may be between

100-220 ppm and between 50-80 ppm at low rate. This is due to compounds used during
manufacture curing within the combustion chamber. On boilers which have been fired for more than
one hour since installation, the CO levels should not exceed 150 ppm at high rate and 50 ppm at low
rate. If CO levels above these values are experienced, the combustion chamber and flue system
should be investigated.

The C110 & C90 are factory set for combustion and should need no adjustment. However, in the

event adjustment is required.

Check combustion errors are not a result of incorrectly installed flue and/or air system, terminal

location or damage or debris on the burner. If all these factors are found to be in order precede as
follows:

1) Set any controls to call for heat.

2) Set the boiler to run at maximum / minimum fan speed. To do this is necessary to access the

hidden buttons (behind the “KESTON” label under the display). There are five buttons, which
are used to adjust settings and provide additional boiler information. The drawing below
shows the layout of these buttons and their function:
To set the fan to maximum.
Press the “Mode” button
repeatedly until the display shows
“Stby”. Press and hold the “Mode”
and “+” key together for 2
seconds. The display will then
show “H nn”. The unit is now
locked on max fan speed.

3) Measure the CO2 reading in the
flue gases and adjust, if necessary, the
adjustment screw (pos.5) to produce a
CO2 reading of 8.2% to 8.7% for C90 and

8.6% to 9% for C110 with a corresponding
CO level of 50 to 150 ppm for natural gas.
NORMAL ADJUSTMENT, IF REQUIRED,
SHOULD NEED NO MORE THAN HALF
OF ONE ROTATION OF THE ADJUSTMENT SCREW (pos.5).

To set the fan to minimum

Press the “Mode” button repeatedly until the display shows “Stby”. Press and hold the “Mode”
and “-“ keys together for 2 seconds. The display will then show “L nn”. The unit is now locked
on min fan speed.

4) Measure the CO2 reading in the flue gases. The CO2 reading must be 8% to 8.2% for C90
and 8.3% to 8.5% for C110 with a corresponding CO level of 5 to 20 ppm for natural gas. THE CO2
LEVEL AT LOW RATE MUST ALWAYS BE LESS THAN THE CO2 LEVEL AT HIGH RATE.

If following the above procedure, combustion levels described above at both high and low rate

could not be obtained, please turn off the appliance and isolate the gas to the appliance.
Telephone KESTON BOILERS technical support (phone no. 0208 462 0262)

To revert to normal modulation

Press the “Mode” button repeatedly until the display shows “Stby”. Press and
hold the “+” and “-“ keys together for 2 seconds.

2/2