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.

Installation & Servicing Instructions Page : 10

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.

Installation & Servicing Instructions Page : 11