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

Page : i

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

Page : ii

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

Installation & Servicing Instructions Page : 1

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.

Installation & Servicing Instructions Page : 2

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

Installation & Servicing Instructions Page : 3

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

Installation & Servicing Instructions Page : 4

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.

Installation & Servicing Instructions Page : 5

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)

Installation & Servicing Instructions Page : 6

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.

Installation & Servicing Instructions Page : 7

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.

Installation & Servicing Instructions Page : 8

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.

Installation & Servicing Instructions Page : 9

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.

Installation & Servicing Instructions Page : 10

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.

Installation & Servicing Instructions Page : 11

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