Keston K340, K260 User Instructions

WD53/0/1999 The Keston 260 & 340 Condensing Boilers

Fan Powered High Efficiency

Commercial Condensing Gas Boiler

Installation And Servicing Instructions

Keston 260
Keston 340

PI No : 87AU111 GB/IE

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]

e-mail: [e-mail] http: //www.keston.co.uk

0087

WD53/0/1999 The Keston 260 & 340 Condensing Boilers

CONTENTS

Section Description
1 GENERAL INSTRUCTION

1.1 Description

1.2 Boiler Schematic

1.3 Related Documents

1.4 Performance Data

2 BOILER LOCATION

2.1 Dimensions & Minimum Clearances

2.2 Service Connections

2.3 Position

2.4 Electrical

2.5 Gas Supply

2.6 Water Systems

2.7 Flue System

2.8 Air Supply

2.9 Compartment Installation

2.10 Condensate Drainage

2.11 Under Floor Heating/Weather Compensation

3 INSTALLATION OF THE BOILER

3.1 Wall Mounting Bracket

3.2 Mounting The Boiler

3.3 Floor Standing Frame - 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

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 Checking The Gas Pressure

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WD53/0/1999 The Keston 260 & 340 Condensing Boilers

4.7 Combustion Fine Tuning

4.8 Handing Over To The User

5 FAULT FINDING

5.1 Electrical Control Sequence

5.2 Fault Finding Flow Chart

5.3 Continuity Checking

5.4 Module Functional Flow Wiring Diagram

5.5 Full Electrical Wiring Diagram

5.6 Full Illustrated Wiring Diagram

5.7 Exploded Assembly Diagrams

6 SERVICING

6.1 Pre Service Checks

6.2 Recommended Routine Service

7 REPLACEMENT OF PARTS

7.0 General

7.1 Precautions

7.2 Access

7.3 Replacement Procedure

7.4 Electrical Components

7.5 Gas Orifice

7.6 Spark Ignition/Flame Detection Electrode

7.7 Burner Head & Burner

7.8 Heat Exchanger

7.9 Condensate Trap

7.10 Pressure Gauge

7.11 Sight Glass

7.12 HT Ignition Lead

7.13 Air Orifice

8 SPARE PARTS LISTINGS

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WD53/0/1999 Chapter 1 : General Instruction The Keston 260 & 340 Condensing Boilers

1. GENERAL INSTRUCTION

1.1 DESCRIPTION

The Keston 260 and 340 Condensing Boilers are unique in their concept and design. They
comprise two boiler m odules with individual gas valve, fans, bur ners and heat exchanger
assemblies. The two modules are fully independent in operation and are automatically
sequenced to provide optimum load matching. In addition, firing sequence is regularly
rotated to ensure even usage levels. While the application for which the boilers were
designed is the same as those which other boilers are used, the Keston boiler has the
added advantage of very high efficiency, and small diameter plastic flue which can be
extended to 20 metres horizontally or vertically. The Keston 260 and Keston 340 are
designed to be wall hung. However, floor standing installation can be accomm odated by
using the optional floor standing frame.

The Keston module uses a high power combus tion blower to deliver a pre-mix of gas and
air to a downward firing burner in a high efficiency, single pass heat exchanger. The flue
system is room sealed and f an powered. The ignition is direct spark and f ully automatic.
The boiler housing is not waterproof and should be installed in a position where it will
always be dry. Consideration should also be given to the noise levels generated by the
combustion fan when in operation. Small air intake points are incorporated within the
appliance cabinet to ensure that the interior of the cabinet is maintained under a slight
negative pressure. This is a safety feature to reduce the possibility of products leak age
out of the cabinet into the installation space..

The boiler is suitable for c onnection to open vented or, preferably, sealed systems. The
system must be pumped centra l heating or pum ped c entr al heating with combined indirec t
sanitary hot water. Gravity circuits must not be used.

Forming part of each boiler m odule is the heat exchanger which is made from a highly
corrosion resistant stainless steel, formed into tightly wound coil. The hot combustion
gases from the c entral down firing burner pass through this coil imparting heat into the
system water. Integral module shunt pumps within the appliance cabinet ensure each
module receives correct water flow when firing. The Keston boiler is not a high water
content boiler and does not contain the m etal mass, or water volume, of a cast iron or
steel boiler. This boiler is of low mass and low water content and therefore responds
faster when there is a call for heat.

1.2 BOILER SCHEMATIC

Air is drawn into the boiler through a 100mm com pos ite plastic pipe. Eac h m odule air flow
is proved by a differential pressure across the air control orifice. Gas is mixed with
combustion air at the inlet to the fan. The gas flow is regulated by an orifice located in the
housing downstream of the gas valve. T he gas and air are thor oughly 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 coil at the bottom of the heat exchanger.

When the return water temperature is below 55
combustion products will condense ins ide 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
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.

o

C, part of the water vapour in the

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WD53/0/1999 Chapter 1 : General Instruction The Keston 260 & 340 Condensing Boilers

Fig. 1.2 - Boiler Layout

The condensate is very slightly acidic with a pH level of around 5 (about the sam e 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 100mm composite plastic pipe to the outside. The
temperature of the flue gas es are usually around 5
water. The flue pipe should be term inated outside the building from where they cannot
re-enter the building or any other adjacent building.

The heating level m ay be controlled by room thermostats, hot water ca lorif ier ther mostats,
programmer time clocks and energy management systems.

1.3 RELATED DOCUMENTS

The Keston Condensing Boiler must be ins talled in accordance with the current issue of
the Gas Safety (Installation and Use) Regulations (as amended after 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 boilers of rated input

BS 6880 : Central Heating by LPHW
BS 7593 : Treatment of Water in Hot Water Central Heating

o

C above the temperature of the return

between 60kW and 2MW

Systems.

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WD53/0/1999 Chapter 1 : General Instruction The Keston 260 & 340 Condensing Boilers

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)

BS 7593 : Treatment of Water in Hot Water Central Heating

Systems
For Timber Framed Buildings please refer to The Institute of Gas Engineers
document IGE/UP/7:1998.

1.4 PERFORMANCE DATA

KESTON 260 KESTON 340

Max. Input (Gross CV) kW/(Btu/h) 84.6/(288,650) 110/(375,300)
Max. Output To Water (80/60C Flow/Return) kW/(Btu/h) 76.1/(259,650) 99.0/(337,800)

Max. Output To Water (60/40C Flow/Return) kW/(Btu/h) 79.5/(271,250) 104.0/(354,800)
Max. Output To Water (50/30C Flow/Return) kW/(Btu/h) 82.9/(282,850) 107.8/(367,800)
Burner Setting Pressure - Hot (Factory Preset) mbar/(in w.g) 9.8/(3.9) 13.0/(5.2)

3

Gas Consumption After 10 mins l/s / (Ft
(CV of Gas - 38.7 MJ/m
Max. Operating Flow Temp.

3

) / (1038 Btu/Ft3)

o

C 82.00 82.00

/hr) 2.19/(278) 2.84/(362)

Max. Head (Open Systems) m / (ft) 30.50 / (100) 30.50 / (100)
Max. Press. (Sealed System) Bar 2.70 2.70
Min. Head (Open Systems) m 3.0 3.0
Inlet Gas Pressure mbar/(in w.g) 20.0 / (8.0) 20.0 / (8.0)
Gas Orifice Size mm 3.75 4.75

o

Recommended Temperature Differential

C 10 to 15 10 to 15
Required Water Flow Rate l/s 1.6 2.0
Electrical Supply 230V 50Hz 230V 50Hz
Power Consumption (Max) W 1200 1200
Cabinet Height mm 1262 1262
Cabinet Width mm 1082 1082
Cabinet Depth mm 354 354
Weight - Full kg / (lbs) 165/(363) 165/(363)
Weight - Empty kg / (lbs) 150/(330) 150/(330)
Flow and Return Connection Rp 2" F Rp 2" F
Gas Connection Rp 1.25" F Rp 1.25" F
Flue Pipe Size (nominal bore) mm / (in) 100 / (4) 100 / (4)
Air Intake Pipe Size (nominal bore) mm / (in) 100 / (4) 100 / (4)
Max. Air Intake Length m 20.0 20.0
Max. Flue Outlet Length m 39.0 39.0
Max. Total Flue Outlet and Air Intake Length m 40.0 40.0
Type of Gas G20 Natural Gas Only
Flue & Air Intake Pipe Material Keston Composite Pipe Only
Optimum Flue Gas CO2 Level % 8.4 8.4
Destination Countries GB/IE GB/IE

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

2. BOILER LOCATION

2.1 DIMENSIONS AND MINIMUM
CLEARANCES

The boiler must be installed in m inim um
clearances shown to allow subsequent
servicing, and safe operation.

2.2 SERVICE CONNECTIONS

Gas, water, air and flue pipe,
condensation, and electrical
connections are as shown. Gas : 1.25
inch BSP female. Flow/Return 2 inch

BSP female.

2.3 POSITION

The Keston is 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.

All dimensions in mm.

1

540

127

127

1

Figur e 2.1.1

Minimum Clearances

Compartment installation is
permitted - such compartments
must be constructed in
accordance with BS 6798.

The wall on which the boiler is
mounted must be of suitable load
bearing capacity and must be
non-combustible.

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

The Keston 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.

Figure 2.1.2

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

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 230V ~ 50Hz supply/controls as follows:

Mains Connection (rated at 10A)

On/Off User Control Link (volt free external control)

Remote Lockout Signal

Main System Pump (optional)

Terminal 1 - LIVE
Terminal 2 - NEUTRAL
Terminal 3 - EARTH

Terminal 17
Terminal 18

(230V)
Terminal 19 - Module 1
Terminal 20 - Module 2
NB: External monitoring controls must be configured to ignore

signal unless present for more than 5 seconds.

[pump on when boiler enabled]
Terminal 4 - Live
Terminal 6 - Neutral
Terminal 7 - Earth

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 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 10A supply via a fused
double-pole switch having at least 3mm (1/8 inch) contact separation in both
poles, serving only the boiler and the system controls.

2.5 GAS SUPPLY

A gas meter should be connected to the service pipe by the local gas supplier 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. Gas consumption is given in Section 1.4.
The boilers are for use with NATURAL GAS (G20) ONLY.

Minimum/Maximum Natural Gas Pressure:

Natural gas pressure before the gas valve must be maintained at between 17.5 mbar (7 in
WG) and 22.5 mbar (9 in WG) while both modules are running.
Gas pressures above or below this level 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
(1.25 in). 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
ignition failures. Ensure gas supply pipe work is adequately sized for the length of
run from the meter to the boiler.

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

2.6 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.
Water treatment must be carried out to BS 7593 : Treatment of Water in Hot Water
Central Heating Systems.
Pump isolating valves must be positioned as close to the pump as possible.

a The Keston 260 and 340 are suitable for use on open, vented water systems with

combined feed and vent of 32mm nominal diameter.

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.

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

connection with the boiler. A strainer should be installed in the system return 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.

Expansion
Pipe

Boiler

IV

Keston

3 Way
Valve

Drain

32mm

Minimum
dia.

IV

Low loss
header

IV

Expansion
Tank

Pump

Strainer

DOC

Minimum
9ft Height

IV

Figure 2.6.1
Open Vented System

System flow(s)

IV

System return(s)

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

2.6.1 Open Vented Systems

A typical system is shown in Figure 2.6.1 which includes a combined feed and
vent. Note 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 system pipework. If the cold feed/vent is not brought to the low loss header
as shown, then the pressure loss across the heat exchanger may have to be
taken into account when estimating the static pressure. Cold feed/vent size must
comply with BS6644.

Although suitable for open vented systems with combined feed and vent
arrangements, the Keston is a low water content boiler. 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.

Safety Valve

Boiler

Keston

2.6.2 Sealed Systems

Sealed systems must be designed in accordance with BS 6644 and BS 7074 Pt1.
A typical sealed system is shown in Figure 2.6.2. It must include :

IV

IV

AV

Low loss
header

IV

IV

DOC

Pump

Strainer

IV

System flow(s)

IV

System return(s)

Fill Point

Expansion
Vessel

Figure 2.6.2
Sealed System

(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 on the basis of

the total system volume and initial charge pressure. The vessel must be

positioned as shown in figure 2.6.2.
(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) The installation must be designed to work with flow temperatures of up to

110

o

C.

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

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

2.6.3 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.

2.6.4 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 meet the minimums required by the
boiler the boiler will “kettle” or even produce steam which can damage the heat
exchanger and invalidate the heat exchanger warranty. The implementation of a
balance header, as shown in the above schematics, is recommended to ensure
adequate water circulation is maintained through the boiler by the integral boiler
shunt pumps, irrespective 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 Header Diameter
up to 100kW 3”
up to 200kW 4”
up to 300kW 4.5”
up to 400kW 5”

o

C.

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

header pipe. Common flow and return connections with 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.

2.6.5 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.

2.6.6 Strainers

Debris in the heating system can cause noise if it enters the heat exchanger.
Fitting of a Y-strainer on the system return(s) will trap any debris left in the
system. The boiler guarantee does not cover heat exchanger failure due to debris

abrasion within the system.

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

2.6.7 Pump Selection

The Keston 260 and Keston 340 boilers are supplied complete with integral boiler
shunt pumps. However, these pumps are sized purely to provide adequate flow
rate through the boiler at the pressure drop caused by the boiler itself. No
allowance has be provided in the shunt pump size for system resistance.

A system pump(s) should therefore be selected sized to provide the required
system flow rate at the pressure drop created by the system index circuit.

2.7 FLUE SYSTEM

2.7.1 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 not less than
100mm. Suitable pipe and fittings
can be obtained by Keston Boilers
Ltd via its appointed distributors.

Both flue outlet terminal and air
inlet terminal are supplied and are
illustrated in Figure 2.7.1.

Although the flue outlet and air
inlet terminals are identical great
care must be taken to ensure that
the air intake terminal is positioned
facing downwards or 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.

2.7.2 Minimum & Maximum Lengths

The flue outlet and air inlet pipes must have lengths of at least 1m each.
The maximum lengths of both air inlet pipe and flue outlet pipe, when no bends

are used, are as detailed below.
Minimum Flue Length : 0.5m

Minimum Air Intake Length : 0.5m
Maximum Air Inlet Length : 20.0 m

Maximum Flue Outlet Length : 39.0 m
Maximum Combined Air Inlet : 40.0 m
and Flue Outlet Length

Figure 2.7.1
Terminal Design

However, each bend used has an equivalent length that must be deducted from
the maximum straight length stated above. Knuckle bends must not be used.

o

A 92.5

sweep elbow is equivalent to 1.0m straight length.

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

Example:
Air inlet uses two

one 92.5
elbows. Hence,
maximum length
permissible (ie a+b
in figure 2.8.2) =

20.0m - 1.0m - 1.0m
= 18.0m

Flue outlet uses one

92.5
Hence, maximum
length permissible
(ie c+d in figure 7 =

40.0m - 1.0 m - total
air inlet length =

39.0m - total air inlet
length.

2.7.3 Slope

'Horizontal' flue outlet pipework
MUST slope at least 2.5
degrees (45 mm per metre
run) downwards towards the
boiler. 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
prevented from entering the
pipe. There must be no

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

o

sweep

o

sweep elbow.

FLUE

d

c

Figure 2.7.2 : Flue & Air Maximum Length Example

To Terminal

To Boiler

be

AIR

b

a

Keston

Figure 2.7.3:
Flue Condensate Drain
Point Example

Tee Fitting

6 in min.

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 4m. These
additional condensate drains must be run to discharge as detailed in section 2.10.
Such drain points can be formed using standard Keston Composite flue fittings.
Refer to the example in Figure 2.7.3.

2.7.4 Terminations
Air inlet terminals must be facing downwards and positioned to ensure only fresh

air is drawn into the boiler. The air terminal must be located outside of the
building.

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

The air inlet terminal must face downwards to prevent entry of rain into the air
intake pipework.

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

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 inlet 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.
If either the air inlet or the flue outlet terminate at a height of less than 2m (6ft)
above ground level the termination must be protected by a suitable guard.
Suitable terminal guards can be obtained from Tower Flue Components Ltd or its
distributors.

The Keston Condensing Boiler, 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.

o

It is advisable for horizontal flue terminals to place a 45

elbow at the end of the

flue to direct the condensate plume up and away from the property.

Dimensions (mm)

etc.

Table 2.7.4 Minimum Flue Terminations & Air Inlet Dimensions

2.7.5 Clearances From Wall

Flue

Terminal

Air

Inlet

50500A Below or beside openable window, air brick,

7575B Below gutters, soil pipes, drain pipes.
50300C Below eaves.
50200D Below balconies or car port roof.
5075E From vertical drain or soil pipes.

50600F From internal or external corner.
100300G Above ground or balcony or roof.
100600H From surface facing a terminal

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.

Flue outlet and air inlet terminations must be at least 60 mm and 95 mm
respectively from the wall face.

2.7.6 Distance Between Flue Outlet & Air Inlet

There is no maximum - the terminations can be on opposite sides of the dwelling
if desired.
A minimum clearance of at least 500 mm must be left between the terminations.

2.7.7 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.

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WD53/0/1999 Chapter 2 - Boiler Connections The Keston 260 & 340 Condensing Boilers

External wall faces and any internal faces of cavity walls must be made good.

2.8 AIR SUPPLY

The Keston is a room sealed appliance and therefore does not require purpose provided
ventilation to the boiler room for combustion air.

2.9 COMPARTMENT INSTALLATION

The casing temperatures of the Keston 260 and Keston 340 are very low. Due to this fact,
no compartment ventilation is required for cooling purposes.

2.10 CONDENSATE DRAINAGE

Being a condensing boiler, the Keston is 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.

Use only plastic piping and do not reduce below 28mm internal diameter within the
dwelling. Condensate should preferably be drained into the sanitary waste system or,
alternatively, the rainwater system of the property.

Termination of the pipe must be either at a branch or stack internal to the building, 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.

2.11 UNDER FLOOR HEATING/WEATHER COMPENSATION

Both underfloor heating and weather compensating control demand reduced system
operating temperatures for some of all of the time the system is operating. Traditionally
this is achieved by used of mixing valves to reduce flow temperature by blending return
water.

The Keston Condensing Boiler provides increased operating efficiencies at low return
system temperature. Therefore, in the event the Keston boiler is serving only underfloor
heating or only weather compensated circuits at any time the boiler flow temperature
should be achieved by limiting the boiler temperature and dispensing with the use of a
mixing valve.

The low operating temperatures of this type of system lead to very good operating
efficiencies. In fact, under floor heating can produce in excess of 95% operating efficiency
from a Keston condensing boiler.

Installation & Servicing Instructions Page : 12

WD53/0/1999 Chapter 3 : Installation The Keston 260 & 340 Condensing Boilers

3. INSTALLATION OF THE BOILER

Read Chapter 2 - Boiler Location and decide upon the position of the boiler.
Installation of the boiler is straightf orward but consideration m ust be given to access to allow f lue
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 bracket, plug the hole and
fix in position.

c Using a spirit level make sure

the bracket is completely level
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

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.

All dimensions in mm.

453

346

553

Figure 3.1 Wall Mounting Fixing Locations

3.3 FLOOR STANDING FRAME - OPTIONAL

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

Remember the flue pipe must
achieved using 92.5

o

bends.

slope downwards back towards the boiler and this is best

Installation & Servicing Instructions Page : 13

WD53/0/1999 Chapter 3 : Installation The Keston 260 & 340 Condensing Boilers

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
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 2.7 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 2.10 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 2.6 Water Systems.
Connections : 2" BSP F.

3.8 GAS SUPPLY

Connect the gas supply to the appliance. Details of gas supply requirements are given in
Chapter 2 - Section 2.5 Gas Supply. Supply of adequate gas pressure
running) is critical to ensure reliable operation of the boiler.
Connections : 1.25 inch BSP F.

Installation & Servicing Instructions Page : 14

(with the boiler

WD53/0/1999 Chapter 3 : Installation The Keston 260 & 340 Condensing Boilers

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 two cord grip bushes. Feed the cable(s)
through its bush and route inside the cabinet to the connection strip located to the front
bottom right of the cabinet.

1. The electrical supply must be as specified in Chapter 2 - Section 2.4 Electrical
Supply.
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 1.0mm
(material code H05VV-F). Pump wiring from the boiler pump connection should
be in 3 core PVC insulated cable not less than 0.5mm

2

to BS 6500 Table 16

2

to BS6500 Table 16

(material code H05VV-F).

3. The permanent live supply connection may be via a 10 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 2 N - Blue wire (Neutral) for 10A permanent supply
Terminal 1 L - Brown wire (Live) 10A permanent supply
Terminal 3 E - Yellow/Green Wire (Earth)

Terminal 17 & 18 - On/Off User controls volt free control link

The pump cable, if used, must be connected to the pump terminals as follows:­Terminal 6 N - Pump neutral wire (blue)
Terminal 4 L - Pump live wire (brown)
Terminal 7 E - Pump earth (yellow/green)

NB: The system circulating pump should not have a locked rotor current rating

exceeding 2A if powered via Terminal 4 of the boiler main terminal block.

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 3.8

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.

Installation & Servicing Instructions Page : 15

WD53/0/1999 Chapter 3 : Installation The Keston 260 & 340 Condensing Boilers

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

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 4.6
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
carbon dioxide (CO

installations that the combustion quality is checked by measuring the

), or oxygen (O2), level. This procedure is detailed in Section 4.7

2

Combustion Fine Tuning. Badly tuned combustion will lead to reduce the life of the boiler
and invalidate the warranty.

Installation & Servicing Instructions Page : 16

WD53/0/1999 Chapter 4 : Commissioning The Keston 260 & 340 Condensing Boilers

4. COMMISSIONING OF THE BOILER

Important:
This condensing boiler c ontains components which could be dam aged or block ed 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 are either copper, bronze or high alloy stainless steel. As
a result standard water treatment chemicals for conventional central heating boilers 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

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.
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 2.6 - 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

link the flow and return pipes on 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 burners requires a special procedure, outlined
below, which must be carried out.

a. Purge the gas supply in accordance with BS 6891 & IM/2.
b. Vent the water system.

Important:

Keston heat exchanger module consists of a single coil which can trap an air

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

exchanger could damage it.
c. Turn both the integral gas service cocks to ON.
d. Turn on the electrical supply, setting any external controls to call for heat.
e. Set the main boiler On/Off switch to “ON” and adjust the set point temperature to

a value above actual flow temperature. (adjustment is made by holding in the

press button located below the control knob and adjusting the control knob until

the required set point temperature is displayed. Releasing the press button will

cause the control knob to be ineffective and the display to register actual flow

temperature).

Installation & Servicing Instructions Page : 17

WD53/0/1999 Chapter 4 : Commissioning The Keston 260 & 340 Condensing Boilers

f Set the left hand module on/off switch to "ON". The amber light will illuminate on

the On/Off switch, the red “lockout” light will illuminate for approximately 2
seconds. The module blower and pump will start and, after about 15 seconds, a
spark will light gas at the main burner, provided all air has been purged from the
gas supply to the boiler. When the burner is lit and the boiler is operating normally
the green (run) lamp, the upper lamp adjacent to the flame symbol, will be
illuminated indicating successful ignition (If it does not and the green lamp is
extinguished after 10 seconds, air is indicated - turn off and repeat the
procedure).
If ignition does not occur, the green (run) lamp, the upper lamp adjacent to the
flame symbol, will be extinguished and, at approximately 1 minute intervals, the
electronic ignition system will make two further attempts to light the burner.
If the ignition is successful and the boiler is operating normally, the green (run)
lamp, the upper lamp adjacent to the flame symbol lamp will remain illuminated.
If after three automatic attempts the boiler still fails to ignite, the green (run) lamp,
the upper lamp adjacent to the flame symbol, will be extinguished, the blower will
post purge for 120 seconds and the red (lockout) lamp will illuminate.
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 red (lockout) lamp) refer to Section 5.2 ­Fault Finding Flow Chart.

g Turn of the on/off switch for the left hand module and repeat step (f) for the right

hand module.

h Check for gas soundness between the gas service cocks and connection to

each 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, ie Fernox Supafloc. 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. For sealed

systems, fill to the required Initial Design Pressure.

4.6 CHECKING THE GAS PRESSURE

With each module running measure each
burner pressure at the module burner
pressure test nipple.

The gas setting is factory adjusted to within
the required range and should not normally
need re-adjustment. If the reading is
incorrect then check such factors as
soundness of the air and flue pipe joints
and the gas inlet pressure (20 mbar
required). If all joints are sound and the gas
inlet pressure is satisfactory remove the
brass dust cap covering the burner
pressure adjustment screw on the gas
valve (See fig. 4.6). Set the gas pressure to
the required value as stated on the
databadge by turning the exposed burner
pressure adjustment screw (clockwise will increase burner pressure, anti-clockwise will
decrease burner pressure). This will ensure that combustion is good enough to allow
combustion fine tuning to take place. Replace the brass dust cap to cover the burner
pressure adjustment screw.

Fig 4.6
MODULE GAS
VALVE

Burner pressure
Adjustment

Burner pressure
test nipple.

Installation & Servicing Instructions Page : 18

WD53/0/1999 Chapter 4 : Commissioning The Keston 260 & 340 Condensing Boilers

4.7 COMBUSTION FINE TUNING

Although the gas pressure is preset at the factory differing flue arrangements may require
fine tuning of the gas pressures to produce the best combustion and ensure long burner
life. It is advisable to check proper combustion by measuring gas input and the level of
carbon dioxide, or oxygen, in the flue outlet from the boiler. Overfiring or underfiring the
burner will reduce the longevity of the appliance.

Carbon dioxide is a colourless, odourless gas produced by all combustion processes.
When the Keston condensing boiler is operating properly carbon dioxide (CO

be between 8.2 and 8.5% CO

for natural gas.

2

) levels will

2

To measure CO

levels in the Keston boiler remove the 1/8" plug from the flue outlet pipe

2

inside the boiler (item 101, fig. 5.7.2). Insert the probe of a combustion analysis meter and
sample the gases as instructed in the test equipment's instructions.

If the CO

levels need raising increase the gas output by turning the brass screw, under

2

the metal cap in the front of the gas valve, clockwise. Reduce CO
screw anti-clockwise.

levels do not respond to adjustments the burner is probably running with too much

If CO

2

gas pressure. If, for instance, a clockwise adjustment to the brass screw in the gas valve
produces a decrease in CO

the burner is too fuel-rich and not enough oxygen is present

2

for proper and complete combustion.

4.8 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 a red light only is illuminated for more than 10 seconds, this means that the

module has failed to light. Turn off the module and wait 20 seconds. Turn ON

again 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 module 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 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 frost precautions.
f. Hand over User Instructions.

levels by turning this

2

Installation & Servicing Instructions Page : 19

WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

5. FAULT FINDING

5.1 ELECTRICAL CONTROL SEQUENCE

When the power supply is established to the boiler and the main boiler on/off switch is in
the "on" position the main on/off switch will be illuminated. Subsequently when the
external controls are calling for heat, power will be fed back to the boiler connection strip
at terminal 18. If the integral sequence controller detects the boiler flow temperature is
below the required set point, one of the modules will be enabled causing that modules
on/off switch, subject to being in the "on" position, to be illuminated. Provided all module
temperature thermostats and pressure switches are closed, power will be fed to pins 1 & 2
on the module ignition control box, initiating the following sequence.

(1) The module lockout lamp (red) will be illuminated
(2) The fan will start.
(3) When the fan reaches running speed, the Air Pressure switch, normally open, will

close which will start the ignition sequence and extinguish the red lockout lamp.
(4) After a pre-purge period of about 15 seconds, the module 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.
(5) When the burner ignites, the flame is detected by the control box through the

combined flame sensor/ignitor and the ignition spark is stopped. The boiler run

lamp (green), the upper lamp adjacent to the flame symbol, will be illuminated.

The boiler is now in its normal run condition.
(6) The burner will continue to operate until the gas valve interrupts the gas supply.

The gas valve will be closed by the control box 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 module will make two further attempts to ignite at intervals

of approximately 1 minute and will then go to a lockout state (red lamp illuminated

only). Once the gas supply has been resumed the module can be reset by turning

the module off and then on again on the boiler control panel.
(7) The module can also be shut down by any of the flow limit, flow overheat and the

flue overheat thermostats, gas low pressure switch and by the low water pressure

switch.

In such an event the green (run) lamp, the upper lamp adjacent to the flame

symbol, will be extinguished and only the red (lockout) lamp will be illuminated.
Dependant on the system loading the integral boiler sequence controller may enable the

other module at any time, subject to that modules on/off switch being in the "ON" position.
The sequence of operation shall be identical to that described above.

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.

Installation & Servicing Instructions Page : 20

WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

5.2 FAULT FINDING FLOW CHART

START

Apply power

to boiler

Is main on/off switch

light on ?

N Y Y

Is main on/off switch

in "on" position ?

Y

Is there 230VAC between

connector strip terminal s 1

and 2 ?

N

N

Switch On

Check external

power suppl y.

Faulty switch neon -

Replace switch.

Y

Continued on
Sheet 2

Set external controls to on

and turn off other module.

Is module amber switch light

on?

N

Is there 230VAC at

terminal 18 ?

Y Y

Is the module switched on ?

Faulty switch neon -

replace switch.

N

N

Check external controls.

Switch on module.

Installation & Servicing Instructions Page : 21

WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

Continued from
sheet 1.

Is the module fan running ?

N Y Y Y N Y Y N N

*

Is the integral sequence controller

calling the module o n ?

N

Boiler f low is too h ot.

Adjust set point higher or

allow to cool or

faulty sequence control.

Is the module return
thermostat closed ?

Is there 230VAC between control

box pins 10 & 2 and between

pins 10 & 1?

Is the air pressure switch

stuck in the NO position ?

Is there 230VAC between control

box pin 6 and neutral ?

Is the fan motor relay operating ?

Is there continuity between the live

supply from relay to blower and

neutral through the motor resistance ?

N

N

Y

N

N

Module return is too hot.

Allow to cool or

faulty thermostat - replace.

Check continuity (see

section 5.3).

Fault hose connection to

APS OR

Faulty APS - Replace

Control box faulty

Relay not secure in socket

Or relay faulty - replace.

Y

Motor/Fan f a ulty -

replace

Continued on
Sheet 3

Is the motor overload tripped ?

(Motor will cycle r apid ly )

Is there wiring continuity through

the in-line connector to the motor ?

* The integral sequence control can be temporarily by-passed for fault diagnosis purposes
by moving the module link wire from module terminal 8 to module terminal 7.

Y

Wait for motor to cool.

Identify & correct break

N

Installation & Servicing Instructions Page : 22

WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

Continued from
Sheet 2

YES

Does the module ignition

sequence start ?

N N Y N Y N N N

Is the fan motor relay stuck ?

Is the module lockout light on ?

Has the module air pressure

switch changed over ?

Are the tubes and connections

to the air pressure switch sound?

Is the air pressure across the

Air Pres sure Switch mor e than

4 inches WG?

Is the air inlet, exh a ust o r

condensate pipe blocked ?

Y

N

N

Y

Switch off & if proble m

Y

Correct tube connection

Faulty pressure switch

Y

Replace Relay.

pers isit s repla ce

control box.

Faulty control box

- replace

- Replace

Clear Blockage

Continued from
sheet 1.

Continued on shee t 4

Is the burner blocked ?

Fan faulty - change

Is the gas flow rate to

the boiler correct ?

N

Is the gas supply pressure

at the module gas valve

correct ?

Y

Clear BlockageY

N

Check gas supply or

turn on module gas cock.

From Sheet 4

Installation & Servicing Instructions Page : 23

WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

Continued from
Sheet 3

Is module burner setting

pressure as per spec.

(Section 4.7)?

Y N N

Is the gas valve opening?

Is there 230VAC at the valve

when the green module run

lamp is lit?

Faulty module control box

- Replace

Is there a spark present ?

N Y Y

Continued on
Sheet 3

N

Y

Y

Adjust burner pressure

Faulty gas valve or

solenoid - replace.

Faulty gas valve or

solenoid - replace

Y

Continued on sheet 5

Is the HT voltage present

at the top of the

ignition electrode?

Is the spark gap 4mm ?

Electrode faulty -

Replace

Does the burner ignite?

N

Recheck gas output pressure.

Check HT lead is securely

fixed. Clean or replace burner.

N

N

Faulty HT lead or

control box - Replace.

Replace/Adjust Ignitor

Installation & Servicing Instructions Page : 24

WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

Continued from sheet 4

Does flame stop after

5 to 10 seconds ?

Y Y N Y

Is boielr earthed correctly?

Are live and neutral supply

lines crosse d at main
connection to boiler?

Is combustion and gas rate

set correctly?

Faulty control box

- Replace

N

Y

N

Earth Boile r

Corre ct Wir ing .

Set gas rate & combustion

(Sections 4.7 and 4.8)

Installation & Servicing Instructions Page : 25

WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

5.3 CONTINUITY CHECKING

To check continuity connect one probe to a neutral and
use the other probe to check 230V AC

START

Is there 230V at

terminals 1, 17 & 18?

Y Y

I s there 230V at the module ON/OFF

sw itch (both terminals) ?

I s there 230V at the module

return thermostat (both

terminals) ?

Y

I s there 230V at the module

flue protection thermostat

(both terminals) ?

Y Y Y

Is there 230V at the gas

low pressure switch

(both terminals) ?

N

N

N

N

Check external controls

and supply.

N

Faulty switch -

Replace

Module is up to tem p erature.

Allow to cool O R pum p n ot

running OR faulty thermostat OR

faulty sequence controller ** -

Replace

Thermostat tripped.

Check thermostat, heat exchanger

and combustion.

C h eck ga s supply to boil e r

OR faulty sw itch - Replace

I s there 230V at the module

wate r pressure switch

(both terminals)?

Is there 230V at the flow

overheat thermostat

(both terminals) ?

Y

Is there 230V at the flow high

limit therm ostat (both terminals) ?

Y

I s there 230V at the module

thermal fuse links

(all terminals)?

N

N

N

Check water level in header tank

O R system pressure O R faulty

switch - replace.

Thermostat tripped.

Check flow rate, reset thermostat

OR faulty thermostat - Replace

N

Hi gh water temperature OR
faulty thermostat - Replace

High cabinet temperature.

Check all joints for product leakage -

reaplce therm al fuse link(s).

** The sequence controller can be temporarily by-passed by moving the link between terminals
8 and 9 on the module terminal block to terminals 7 and 9.

Installation & Servicing Instructions Page : 26

WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

5.4 MODULE FUNCTIONAL FLOW WIRING DIAGRAM

Main On/Off
Switch

230V 50Hz

Sequence
Controller

Module
ON/OFF
Switch

Flue Overheat Thermostat

Low Gas Pressure Switch

Low Water Pressure Switch

Flow Overheat Thermostat

Flow High Limit Thermostat

EMC
Filter

Blower
Relay

Lockout
Relay

Lockout

Lamp

Return

Thermostat

Blower

Lockout

Relay

Coil

Module
Shunt
Pump

Thermal Fuse Links

Run
Lamp

2

5

Gas
Valve

RAM CONTROL BOX

10

HT

8

1
4
6

Blower
Relay
Coil

Air
Press

Switch

N

EMC Filter

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WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

5.5 FULL ELECTRICAL WIRING DIAGRAM

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WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

5.6 ILLUSTRATED WIRING DIAGRAM

Installation & Servicing Instructions Page : 29

WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

5.7 Exploded Assembly Diagrams

5.7.1 Casing Assembly

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WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

5.7.2 Waterway, Condensate & Flue Assembly

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WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

5.7.3 Air - Gas Assembly

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WD53/0/1999 Chapter 5 : Fault Finding The Keston 260 and 340 Condensing Boiler

5.7.4 Controls Assembly

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WD53/0/1998 Chapter 5 : Fault Finding The Keston 260 & 340 Condensing Boiler

5.7.5 Exploded Diagrams Parts Reference List
Casing Assembly (Fig 5.7.1)

GC Number Code Description

- 4 Cabinet

- 40 Name Plate

- 12 Front Panel

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

114 115 77 Heat Exchanger

- 74 Burner
114 118 73 Burner Head Gasket
114 028 71 Sight Glass
375 527 68 Ignitor Gasket
114 120 67 Spark Ignition Electrode
114 029 69 Pressure Test Nipple

- 90 Condensate Trap
375 530 84 Boiler Return Thermostat
375 532 86 Flue Overheat Thermostat
114 043 101 Combustion Test Plug
375 533 97 Flow Overheat Thermostat
375 534 99 Flow High Limit Thermostat
114 045 88 Water Pressure Switch

Frame

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

114 131 154 Combustion Blower

- 163 Air Orifice
375 536 136 Gas Valve
114 029 69 Pressure Test Nipple
114 073 134 Low Gas Pressure Switch

- 144 Gas Injector

Boiler Controls Assembly (Fig. 5.7.4)
GC Number Code Description

- 217 Sequence Controller
E01-074 183 Ignition Control Box

- 202 Air Pressure Switch

- 205 Electrical Terminal Block

- 215 Main On/Off Switch

- 214 Module On/Off Switch

212 Module Green (Run) Lamp
213 Module Red (Lockout) Lamp

114 080 211 Pressure Gauge

Installation & Servicing Instructions Page : 34

WD53/0/1999 Chapter 6 : Servicing The Keston 260 & 340 Condensing Boilers

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.

6.1 Pre-Service Checks

It is recommended that an inspection should be carried out prior to shutting down the unit
for servicing. Open the front doors by turning the door catches 90 degrees. The following
items should be observed:
a. Smooth starting and running of each modules blower.
b. Smooth lighting of each modules burner.
c. Check for leakage of gas, gas/air or combustion products.
d. Check for condensate leaks.
e. Check the colour and appearance of the flame on each module. A sky blue flame

slightly off the burner gauze is normal. The burner itself should appear dark.

f. Check that the temperature differential between the flow and return pipes is less

than 15
g. Check for water soundness.
h. Inspect the flue vent and air intake pipework. Joints must be sound and all

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

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

that the condensate flows freely from the condensate line.

o

C. The temperature difference should be between 10oC and 15oC.

o

C) check

6.1.1 Module Burner & Heat Exchanger Blockage Checks

i) Turn off the boiler & shut off the gas supply to the boiler.

ii) Remove the pressure point screws from points A & B on the heat

exchanger for the left hand module. Attach a differential gauge.

iii) Turn on the boiler and wait for the fan to reach full speed. Obviously the

burner will not light.

iv) The pressure difference should be less than 10.0 mbar. If not clean the

burner.
v) Turn off the electrical supply to the boiler.
vi) Remove the pressure point screw from point C and transfer the tube from

point A to C, replacing the screw on point A.
vii) Turn on the electrical supply to the boiler (gas still off), wait for the fan to

reach full speed.
viii) The pressure difference should be between 9.5 mbar and 13.5 mbar

(lowest value represents new appliance). If not clean heat exchanger.
ix) Disconnect the gauge from point B. Refit the screw.
x) Read pressure of point C.
xi) The maximum pressure should be 3.5 mbar. If the pressure is greater

than this check the flue for blockage.
xii) Turn off the electrical supply to the boiler
xiii) Repeat the procedure for the right hand module.
xiv) Remove the pressure gauge tube and refit the screw.
xv) Open the gas service cock.

Installation & Servicing Instructions Page : 35

WD53/0/1999 Chapter 6 : Servicing The Keston 260 & 340 Condensing Boilers

Pressure Test

Pressure Test

Point A

Point B

Burner Heat (From Above)

Fig 6.1.1 Module Pressure Test Point Locations

6.2 Recommended Routine Service

The procedure detailed below should be carried out on each boiler module in turn. The
integral boiler controller ensures both modules are loaded evenly over a year of operation.
a. Remove the burner head (Section 7.7) and inspect the burner appearance. Black

markings or other discolourations on the gauze indicate too much gas or a lack of
air. Any breakages or damage to the burner mesh indicate the burner must be
replaced.

b. If necessary, either due to discolouration or a high pressure differential between

points A & B in the pre-service checks, clean the burner with a mild
detergent and rinse under a hot running tap.

c. If necessary, either from visual inspection or a high pressure differential between

points B & C in the pre-service checks, 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.

d. Remove the condensate trap (Section 7.10) and clean by flushing through with

clean running water.

e. Check the electrode mounted on the burner head. If the point is damaged or

burnt replace it.
Check that the spark gap measures 4 mm.

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

gas/air supply and the ignition lead. Ensure the flanged gas/air supply joint is air
tight.

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

temperature levels.

h. Visually inspect the burner through the glass spy hole at the burner head (a small

mirror will prove useful).
i. Recheck the burner pressure by following the procedure detailed in Section 4.7
j. Remove the combustion test point plug from the flue pipe. This is situated around

150mm (6ins) from the bottom of the flue elbow at its connection to the heat

exchanger.
k. Using an approved combustion tester sample the flue products via the

combustion test point. CO

If such levels are not observed tune the combustion as described in Chapter 4 -

Commissioning. Also check the gas flow as detailed in Sections 4.8 and 4.9
l. Replace the combustion test point plug.

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

Flue

Heat
Exchanger
Shell

Pressure Test
Point C

&

Combustion
Test Point

Flue Overheat
Thermostat

household

levels of between 8.2% and 8.5% should be observed.

2

Installation & Servicing Instructions Page : 36

WD53/0/1999 Chapter 7 : Replacement Of Parts The Keston 260 and 340 Condensing Boilers

7. REPLACEMENT OF PARTS

INDEX

7.0 GENERAL

7.1 PRECAUTIONS

7.2 ACCESS

7.3 PROCEDURES - GENERAL

7.4 ELECTRICAL

7.4.1 ON/OFF SWITCH

7.4.2 BOILER THERMOSTAT

7.4.3 FLOW OVERHEAT, FLOW HIGH LIMIT & FLUE PROTECTION
THERMOMSTATS

7.4.4 WATER PRESSURE SWITCH

7.4.5 IGNITION CONTROL BOX

7.4.6 AIR PRESSURE SWITCH

7.4.7 COMBUSTION BLOWER

7.4.8 GAS CONTROL VALVE

7.4.9 GAS LOW PRESSURE SWITCH

7.5 GAS ORIFICE

7.6 SPARK IGNITION/FLAME DETECTION ELECTRODE

7.7 BURNER HEAD & BURNER

7.8 HEAT EXCHANGER

7.9 AIR FILTER

7.10 CONDENSATE TRAP

7.11 PRESSURE GAUGE

7.12 SIGHT GLASS

7.13 HT IGNITION LEAD

7.14 AIR ORIFICE

Installation & Servicing Instructions Page : 38

WD53/0/1999 Chapter 7 : Replacement Of Parts The Keston 260 & 340 Condensing Boilers

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
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 turning

the boiler ON/OFF switch to the OFF position. Shut off the power
supply at the isolating switch before working on the appliance.

7.2 ACCESS

i) Open the front doors by turning the locating catches 90 degrees to release.

7.3 REPLACEMENT PROCEDURES

i) Always replace in the reverse order unless otherwise stated.
ii) Electrical connections must be remade in accordance with the 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 Master and Module On/Off Switches (Fig. 5.7.4 items 214 & 215)

i) Isolate the appliance (Section 7.1)
i) Gain access (Section 7.2)
iii) Remove the push on connectors from the switch taking note of the

correct positions.

iv) Press in the catches and push the switch forwards through the control

panel.
v) Reassemble (Section 7.3)
v) Check for correct operation of the switch.

7.4.2 Module Boiler Return Thermostats (Fig. 5.7.2 item 84)
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 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
mounting surface. This, combined with fitting the new thermostat
tightly to the mounting surface, ensures a good contact.

7.4.3 Module Flow Overheat (Fig. 5.7.2 item 97) , Flow High Limit (Fig. 5.7.2 item

99) & Flue Protection Thermostats (Fig. 5.7.2 item 86)
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 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.

7.4.4 Module Water Pressure Switch (Fig. 5.7.2 item 88)
i) Isolate the appliance (Section 7.1)
ii) Shut off the water supply to the appliance.
iii) Gain access (Section 7.2)

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WD53/0/1999 Chapter 7 : Replacement Of Parts The Keston 260 and 340 Condensing Boilers

iv) Drain the system to below the level of the appliance using the drain off

tap at the base of each 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).
viii) Refill the system (See Section 4 - Commissioning).

7.4.5 Module Ignition Control Box (Fig. 5.7.4 item 183)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the HT ignition lead.
iv) Pull off the multi-pin connector away from the box.
v) Unscrew the two screws securing the control box to the casing and

remove the box.

vi) Reassemble (Section 7.3)

7.4.6 Module Air Pressure Switch (Fig. 5.7.4 item 202)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the push on connectors from the air pressure switch taking note

of the correct positions.

iv) Disconnect the union to one plastic tube connection and pull off the

second plastic tube from the air pressure switch.

v) Unscrew the two screws mounting the air pressure switch body to the

boiler casing.

vi) Reassemble (Section 7.3)

NB: Ensure the yellow/green earth connection tag is securely fixed

behind the lower mounting screw.

7.4.7 Module Combustion Blower (Fig. 5.7.3 item 154)
NB: This unit is heavy and must therefore be handled carefully when

replacing.
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Disconnect the wires connecting the blower in the blower motor

connection box.
vi) Remove the allen screws fixing the air intake pipe flange and the gas/air

mixture pipe flange to the blower.
v) Unscrew the three bolts fixing anti-vibration mounts to the combustion

blower through the base of the blower shelf.
vi) Reassemble (Section 7.3)

NB: When reassembling inspect any gaskets for damage and replace

if necessary.

vii) Reset the gas rate (See Section 4 - Commissioning)

7.4.8 Module Gas Control Valve (Fig. 5.7.3 item 136)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the cover concealing the electrical connections on the front of

the gas valve.

iv) Remove the push on connectors exposed taking note of the correct

positions.

v) Remove the push on connectors to the gas low pressure switch taking

note of the correct positions.
vi) Remove the earth connection to the side of the gas valve.
vii) Remove the plastic air tube to the base of the gas valve.
viii) Remove the four allen screws securing the gas inlet flanged connections

to the gas control valve.
ix) Undo the four bolts fixing the base of the gas control valve to the gas

outlet block.
x) Remove the gas valve.
xi) Unscrew the gas low pressure switch at its connection to the gas control

valve body.

Installation & Servicing Instructions Page : 40

WD53/0/1999 Chapter 7 : Replacement Of Parts The Keston 260 & 340 Condensing Boilers

xii) Reassemble (Section 7.3)
xiii) Reset the gas rate (See Section 4 - Commissioning)

7.4.9 Module Gas Low Pressure Switch (Fig. 5.7.3 item 134)
i) Isolate the appliance (Section 7.1)
ii) Gain access (Section 7.2)
iii) Remove the push on connectors to the gas low pressure switch taking

note of the correct positions.
iv) Unscrew the gas low pressure switch from the brass holder.
v) Reassemble (Section 7.3)

7.5 MODULE GAS ORIFICE (Fig 5.7.3 item 144)
i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)
iii) Unscrew and remove the brass plug from the gas outlet block.
iv) Remove the rubber seal from the injector housing.
v) Insert a flat blade screwdriver into the exposed hole and unscrew the gas injector.
vi) Check the injector is the correct size for the boiler size.

vii) Reassemble (Section 7.3)

NB: Ensure that the injector is screwed fully home

viii) Reset the gas pressure and combustion (See Section 4 - Commissioning)

7.6 MODULE SPARK IGNITION/FLAME DETECTION ELECTRODE (Fig. 5.7.2 item 67)
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) Remove the burner head (Section 7.7 steps iv) to vi)).
v) Undo the screws to the spark ignition electrode flange located on the burner

head and withdraw the spark ignition electrode.

vi) 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 burner surface is 4mm.
Distances above or below 4mm will affect ignition performance. If
necessary gently bend the electrode taking care not to damage the
ceramic insulator.

7.7 MODULE BURNER HEAD & BURNER (Fig. 5.7.2 items 72 & 74)
i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)
iii) Remove the pull off HT lead to the spark ignition/flame detection electrode head.
iv) Remove the two allen screws fixing the flange gas/air mixture pipe connection to

the burner head.

v) Remove the five allen screws fixing the burner head to the top of the heat

exchanger.
vi) Withdraw the burner & burner head from the top of the heat exchanger.
vii) Unscrew the burner from the burner head taking care not to damage the burner

mesh. (grip the burner on the collet only).
viii) Reassemble (Section 7.3)

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

necessary.
Set the spark gap as detailed in Section 7.6

ix) Reset the gas rate (see Section 4 - Commissioning)

Installation & Servicing Instructions Page : 43

WD53/0/1999 Chapter 7 : Replacement Of Parts The Keston 260 and 340 Condensing Boilers

7.8 MODULE HEAT EXCHANGER (Fig. 5.7.2 item 77)
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 head (Section 7.7)
v) Drain the system to below the level of the appliance using the drain off tap at the

base of the heat exchanger.
vi) Remove the boiler thermostat (Section 7.4.2)
vii) Remove the push on connectors to the water pressure switch, flow overheat

thermostat, flow high limit thermostat and flue protection thermostat taking note of

the correct positions.
viii) Remove the condensate trap (Section 7.10)
ix) Remove the pressure gauge phial located next to the drain off tap.
x) Disconnect the flow to the heat exchanger at the union on the heat exchanger

flow manifold.
xi) Undo the nut and olive of the isolating valve fitted directly on the heat exchanger

return pipe.
xii) Remove the nut fixing the strap retaining the base of the heat exchanger and pull

out the strap by unhooking it from its fixing behind the heat exchanger.
xiii) Remove the allen screw securing the top of the heat exchanger to its mounting

bracket.
xiv) Remove the heat exchanger assembly by pulling forward at the top and lifting up

and out of the appliance.
xv) Cut the olive from the heat exchanger return pipe and remove the compression

nut.
xx) Reassemble (Section 7.3)
xxi) Recommission (Section 4 - Commissioning)

7.9 CONDENSATE TRAP (Fig. 5.7.2 item 90)
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 condensate line from the base of the flue assembly.
v) Disconnect the condense lines from the projection of the condensate trap from

the base of the cabinet.
vi) Withdraw the condensate trap.
vii) Mop up any spilled condensate.
viii) 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.

7.11 PRESSURE GAUGE (Fig. 5.7.4 item 211)
i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)
iii) Shut off the pressure measurement point at the return drain valve located at the

base of the heat exchanger.

iv) Remove the phial from its mounting at the return pipe entry to the base of the heat

exchanger.

v) Press in the catches and push the pressure gauge forward through the control

panel.
vi) Reassemble (Section 7.3)
vii) Refill the system (See Section 4 - Commissioning)

Installation & Servicing Instructions Page : 42

WD53/0/1999 Chapter 7 : Replacement Of Parts The Keston 260 & 340 Condensing Boilers

7.12 MODULE SIGHT GLASS (Fig. 5.7.2 item 71)
i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)
iii) Unscrew the sight glass fitting from the burner head.
iv) Reassemble (Section 7.3)

7.13 MODULE HT IGNITION LEAD (Fig 5.7.4 item 185)
i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)
iii) Remove the lead from the electrode and the ignition control box.
iv) Reassemble (Section 7.3)

7.14 MODULE AIR ORIFICE (Fig. 5.7.3 item 163)
i) Isolate the appliance (Section 7.1)

ii) Gain access (Section 7.2)
iii) Disconnect the flexible air intake hose from the air/gas manifold (Fig 5.7.3 item

164)
iv) Unscrew the air orifice grub screw (Fig 5.7.3 item 140) to release the air orifice.
v) Lift the air orifice from its seat in the air inlet manifold.
vi) Reassemble (Section 7.3)
NB: When replacing the air orifice ensure that the new orifice is seated with the

chamfer facing upwards.

Installation & Servicing Instructions Page : 43

WD53/0/1999 Chapter 8 : Spare Parts Listings The Keston 260 & 340 Condensing Boilers

8. SHORT SPARE PARTS LIST

Item GC No Part Denomination Item GC No Part Denomination

74 - Burner 73 114 118Burner Manifold Gasket

-

68 375 527Ignitor Gasket 67 -

Ignitor/Sensor Probe

-

110 - Flexible Hose Gasket 84 375 530Boiler Thermostat

86 375 532Flue Thermostat 97 375 533Flow Overheat

Thermostat

Installation & Servicing Instructions Page : 46

WD53/0/1999 Chapter 8 : Spare Parts Listings The Keston 260 & 340 Condensing Boilers

Item GC No Part Denomination Item GC No Part Denomination

99 375 534Flow High Limit Stat 142 375 535Gas Valve Outlet

Gasket

136 375 536Gas Valve

147 114 122Flexible Hose Gasket 183 E01-074 Ignition Control Box

202 - Air Pressure Switch 185 E01-075 HT Ignition Cable

-

Installation & Servicing Instructions Page : 46

WD53/0/1999 Chapter 8 : Spare Parts Listings The Keston 260 & 340 Condensing Boilers

SHORT SPARE PARTS LIST FOR THE KESTON

CONDENSING BOILER RANGE

Item GC No Part Denomination

74 - Burner

­73 114 118 Burner Manifold Gasket
68 375 527 Ignitor Gasket
67 - Ignitor/Sensor Probe

­147 114 122 Flexible Hose Gasket
84 375 530 Boiler Thermostat
86 375 532 Flue Thermostat
97 375 533 Flow Overheat Thermostat
99 375 534 Flow High Limit Thermostat
142 114 139 Gas Valve Gasket
136 375 536 Gas Multifunctional Control Valve
183 E01-074 Ignition Control Box
202 - Air Pressure Switch

­185 E01-075 HT Ignition Cable

Installation & Servicing Instructions Page : 46

KESTON CONDENSING BOILERS

IMPORTANT

KESTON 260 & 340

INSTALLATION KEY POINTS

WD180/0/99

†

†

†

†

†

†

†

†

Read Installation Manual Carefully

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

Ensure that the boiler(s) is connected to the system via a low
loss balance header.

DO NOT remove the dust caps from the air and exhaust pipes
until ready to connect.

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 ie 230V fused at

13A for the permanent live.
Ensure that the external controls are configured to form a link

between terminals 17 & 18 to enable boiler.

†

†

†

†

†
†

†
†

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.

Gravity circuits are not allowed.