Keston C25 Installation Manual

WD209/1/2000 The Keston Celsius 25 & 25P

Fan Powered High Efficiency

Modulating Domestic Condensing Gas Boiler

Installation And Servicing Instructions

Celsius 25 & 25P Models

CE/PI No : 87BL49
GC No : 41-930-06

These instructions must be left either with

the user or next to the site gas meter.

34 West Common Road

Hayes, Bromley, Kent BR2 7BX

Tel. [phone] Fax. [phone]

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

WD209/1/2000 The Keston Celsius 25 & 25P

CONTENTS

Section Description

1 GENERAL INSTRUCTION

1.1 Description

1.2 Boiler Schematic

1.3 Related Documents

1.4 Performance Data

1.5 Optional Accessories

2 BOILER LOCATION

2.1 Dimensions & Minimum Clearances

2.2 Service Connections

2.3 Position

2.4 Electrical

2.5 Boiler Size Selection

2.6 Gas Supply

2.7 Water Systems

2.8 Flue System

2.9 Air Supply

2.10 Compartment Installation

2.11 Condensate Drainage

3 INSTALLATION OF THE BOILER

3.1 Wall Mounting Bracket

3.2 Mounting The Boiler

3.3 Assembly Practice

3.4 Installing Flue And Air Pipes

3.5 Condensate Drainage

3.6 Water System

3.7 Gas Supply

3.8 Electrical Supply

3.9 Exchanging A Boiler

4 COMMISSIONING OF THE BOILER

4.1 Initial Flushing

4.2 Gas Supply

4.3 Electrical Installation

4.4 LPG Gas

4.5 Initial Firing

4.6 Hot Flushing

4.7 Checking The Gas Pressure

Page : i

WD209/1/2000 The Keston Celsius 25 & 25P

4.8 Timing The Gas Meter

4.9 Combustion Testing

4.10 Handing Over To The User

5 FAULT FINDING

5.1 Electrical Control Sequence

5.2 Fault Finding Flow Chart - General

5.3 Fault Finding Flow Chart - Detailed

5.4 Functional Flow Wiring Diagram

5.5 Electrical Wiring Diagram

5.6 Illustrated Wiring Diagram

5.7 Exploded Assembly Diagrams

6 SERVICING

6.1 Pre Service Checks

6.2 Recommended Routine Service

7 REPLACEMENT OF PARTS

7.0 General

7.1 Precautions

7.2 Access

7.3 Replacement Procedure

7.4 Electrical Components

7.5 Spark Ignition/Flame Detection Electrode

7.6 Burner

7.7 Heat Exchanger

7.8 Condensate Trap

7.9 Pump

8 SPARE PARTS LISTINGS

9 GAS BOILER COMMISSIONING CHECKLIST

10 HIGH & LOW COMBUSTION SETTING PROCEDURE

Page : ii

WD209/1/2000 Chapter 1 : General Instruction The Keston Celsius 25 & 25P

1. GENERAL INSTRUCTION

1.1 DESCRIPTION

The Celsius 25 is unique in its concept and design. It comprises a high efficiency stainless
steel heat exchanger coupled with a low emissions burner to deliver ultra high efficiency
condensing mode operation within a compact wall hung cabinet. The unit automatically
adjusts gas and air rate according to demand to give an output in the range of 7.0kW to

25.2kW (natural gas model). The integral standard UPS Grundfos pump is automatically
controlled across the three speeds to best match water flow rate to heat output & further
increase appliance efficiency. While the application for which the Celsius 25 was designed
is the same as those which other boilers are used, the Keston Celsius 25 has the added
advantage of very high efficiency, and small diameter plastic flue which can be extended
up to 60 metres horizontally or vertically.

The Keston Celsius 25 uses a variable speed combustion blower to deliver a premix of
gas and air to a downward firing burner in a high efficiency, single pass heat exchanger.
The flue system is room sealed and fan powered. The ignition is direct spark and fully
automatic. The boiler housing is not waterproof and should be installed in a position
where it will always be dry. Combustion air is drawn from the cabinet which is connected
to outside atmosphere via a small diameter plastic intake pipe. The cabinet therefore
remains under negative pressure at all times the boiler is operating.

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

The boiler heat exchanger is made from highly corrosion resistant stainless steel in
corrugated pipe form which provides massive surface area within a compact dimension.
The hot combustion gases from the down firing burner pass around the stainless steel
pipes imparting heat into the system water. The integral standard 3 speed Grundfos pump
within the appliance cabinet ensures the heat exchanger receives correct water flow when
firing. The Celsius 25 is not a high water content boiler and does not contain the metal
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. The Celsius 25
features full user diagnostics, integral frost protection thermostat, automatic pump and fan
exercise in periods of inactivity, anti cycle control, dry fire protection and connections for
remote lockout and run monitoring.

1.2 BOILER SCHEMATIC

Air is drawn into the boiler through a 50 mm muPVC (BS5255 and/or BSEN1566-1 and
BSEN1329) plastic pipe or, alternatively, via a 75mm composite plastic pipe.. Gas is
mixed with combustion air at the inlet to the fan. The gas flow is automatically regulated by
the gas valve according to the air flow generated by the fan. The gas and air are
thoroughly mixed in the blower and fed into the burner located at the top end of the heat
exchanger module. The gas and air mixture is ignited by a direct spark ignition control
system and burns with a blue flame just off the surface of the burner. As the hot products
of combustion pass downwards, they are cooled by exchanging heat with the circulating
water which enters the heat exchanger at the bottom of the heat exchanger. The optimum
heat input is detected by monitoring flow and return temperatures and is adjusted by
controlling the speed of the fan. The optimum pump speed is also detected and
automatically selected by the boiler.

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

Installation & Servicing Instructions Page : 3

WD209/1/2000 Chapter 1 : General Instruction The Keston Celsius 25 & 25P

Fig. 1.2 - Boiler Layout

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

The flue gases are piped in a 50 mm muPVC (BS5255 and/or BSEN1566-1 and
BSEN1329) plastic pipe or, alternatively, 75mm composite plastic to the outside. The
temperature of the flue gases are usually around 5oC above the temperature of the return
water. The flue pipe should be terminated outside the building from where they cannot
re-enter the building or any other adjacent building.

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

The Celsius 25 features an integral frost protection function which will fire the boiler,
regardless of the external controls, should the boiler temperature fall below 4OC. The
boiler will continue to fire until the boiler flow temperature exceeds 15OC. This is to avoid
damage to the boiler through freezing of boiler water.

The Celsius 25 features an integral pump/fan exercise function which will run the fan and
pump, without firing the boiler, for 5 seconds in the event the boiler is on standby for in
excess of 24 hours without firing. This is to help prevent seizing of fan and/or pump due to
long periods of inactivity.

1.3 RELATED DOCUMENTS

The Keston Celsius 25 Condensing Boiler must be installed in accordance with the current
issue of the Gas Safety (Installation and Use) Regulations 1996, current IEE Wiring

Regulations, Building Regulations, Building Standards (Scotland) Consolidation, and the
Bye Laws of the local Water Undertaking.

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

BS 6891 : Gas Supplies
BS 6798 : Installation Central Heating Boilers
BS 5449 : Installation Pumped Central Heating
BS 5546 : Installation Domestic Hot Water
BS 5440.1 : Flues
BS 5440.2 : Air Supply
BS 7074.1 : Expansion Vessels

Installation & Servicing Instructions Page : 2

SEDBUK

Efficiency

*

90.4%93.3

%

WD209/1/2000 Chapter 1 : General Instruction The Keston Celsius 25 & 25P

BS 7593 : Treatment of Water in Hot Water Central Heating

Systems
For Timber Framed Buildings, British Gas Publications DM2. Also British Gas
Publications 'Guidance Notes For The Installation Of Domestic Gas Condensing
Boilers' and 'Specification For Domestic Wet Central Heating Systems'.

1.4 PERFORMANCE DATA

Celsius 25 Celsius 25P
Nat. Gas (G20) LPG (G31)

Max. Input (Gross CV) kW/(Btu/h) 26.1/(89,000) 25.0/(85,300)
Max. Output To Water

(80/60C Flow/Return) kW/(Btu/h) 23.1/(78,800) 22.7/(77,500)
(50/30C Flow/Return) kW/(Btu/h) 25.2(86,000) 24.8(84,600)

Min. Output To Water

(80/60 C Flow/Return) kW/(Btu/h) 7.0(23,900) 6.8(23,300)

(50/30C Flow/Return) kW/(Btu/h) 7.7(26,200) 7.45(25,400)
Max. Burner Press.-Hot (Factory Preset) mbar/(in w.g) -3.15(-1.26) -4.60(-1.84)
Gas Consumption After 10 mins l/s / (Ft3/hr) 0.68(85.7) 0.313(39.5)
Max. Operating Flow Temp.

o

C 82.00 82.00
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) 37.0(14.8)

Recommended Temp Diffl

o

C 8 to 20 8 to 20
Electrical Supply 230V 50Hz 230V 50Hz
Power Consumption (Max) W 160 160
Cabinet Height mm 621 621
Cabinet Width mm 471 471
Cabinet Depth mm 249 249
Top Clearance mm 150 150
Side Clearance mm 1 1
Base Clearance mm 100 100
Front Clearance (for servicing) mm 305 305
Weight - Full kg / (lbs) 43/(95) 43/(95)
Weight - Empty kg / (lbs) 38/(84) 38/(84)
Flow and Return Connection Rp 0.75" F Rp 0.75" F
Gas Connection Rp 0.5" F Rp 0.5" F
Condensate Connection mm 22mm plastic overflow

Flue and Air Intake Material 50mm muPVC (BS5255 and/or BSEN1566-1 and BSEN1329)
Flue Pipe Size (nominal bore) mm / (in) 50 / (2)
Air Intake Pipe Size (nominal bore) mm / (in) 50 / (2)
Max. Air Intake Length m 39
Max. Flue Outlet Length m 20
Max. Total Flue Outlet and Air Intake Length (m) 40

Flue and Air Intake Material 75mm Keston Composite
Flue Pipe Size (nominal bore) mm / (in) 75 / (3)
Air Intake Pipe Size (nominal bore) mm / (in) 75 / (3)
Max. Air Intake Length m 117
Max. Flue Outlet Length m 60
Max. Total Flue Outlet and Air Intake Length (m) 120

Type of Gas G20 Natural Gas G31 LPG
Optimum Flue Gas CO2 Level % 8.4 10.0
Destination Countries GB/IE GB/IE

Installation & Servicing Instructions Page : 3

WD209/1/2000 Chapter 1 : General Instruction The Keston Celsius 25 & 25P

*) Seasonal Efficiency (SEDBUK) = 90.4% (Celsius 25) and 93.3% (Celsius 25P)
This value is used in the UK Government's Standard Assessment Procedure (SAP) for
energy rating of dwellings. The test data from which it has been calculated have been
certified by Advantica Technologies Ltd
Keston Boilers Ltd declare that there are no substances harmful to health within the
appliance or used during the production of the appliance.
The Celsius 25 is intended for domestic and commercial EMC environments and on a
governed G20 meter supply.
The Celsius 25P is intended for domestic and commercial EMC environments and on a
governed G31 supply.

IMPORTANT
This product contains ceramic fibre boards, which although not regarded as a risk, contain
ceramic fibre which may cause temporary irritation to eyes, skin and respiratory tract. The
fibres are held in place by inorganic binders. Therefore as long as the boards are not
disturbed they will not be released. Since the boards are non-servicable parts there should
be no risk.
To ensure that the release of fibres from these RCF articles is kept to a minimum, during
installation and servicing we recommend that you use a HEPA filtered vacuum to remove
any dust accumulated in and around the appliance before and after working on the appli­ance. When replacing these articles we recommend that the replaced items are not broken
up, but are sealed within heavy duty polythene bags, and clearly labelled as RCF waste.
RCF waste is classed as a stable, non-reactive hazardous waste and may be disposed at a
landfill licensed to accept such waste. Protective clothing is not required when handling
these articles, but we recommend you follow the normal hygiene rules of not smoking,
eating or drinking in the work area and always wash your hands before eating or drinking.

BENCHMARK INITIATIVE

As part of the industry wide “Benchmark” initiative KC25 boiler
manual includes Gas Boiler Commissioning Checklist (Chapter

9). This form should be completed by your installer at the end of the
installation and commissioning process. The details of the Checklist will be required in the event of
any warranty work being required. There is also Service Interval Record (Chapter 9) to be
completed after each annual service visit.

These forms (Chapter 9) should be kept in a safe place for the life of the boiler.
CORGI INFORMATION

The boiler should be installed and serviced only by CORGI registered operatives. All CORGI
registered Installers carry a CORGI ID card and have a registration number. Both should be

recorded in your boiler manual (Chapter 9: GAS BOILER COMMISSIONING CHECKLIST).

You can check your installer by calling CORGI direct on 01256 372300.

1.5 OPTIONAL ACCESSORIES

A range of accessories are available from Keston Boilers Ltd to compliment an installation.
Terminal wall dealing collars are available to make good the external all face whilst working from
the inside of the building using 50mm muPVC (BS5255 and/or BSEN1566-1 and BSEN1329) pipe
or 75mm (actual dimensions are int.dia. = 68mm, ext.dia. = 78mm) Keston Composite pipe.
Stand-off frames are available to leave a 50mm gap behind the boiler to allow routing of pipes
behind the boiler. A sealed system kit is available to mount below the boiler as an extension to the
cabinet and convert the boiler to a "system" boiler incorporating 8 litre expansion vessel and 3 bar
safety valve.

Description Part Number

Flue Terminal Wall Sealing Collar C.08.0.00.07.0
Air Terminal Wall Sealing Collar C.08.0.00.07.0
50/75 Flue Adapter C.17.2.00.60.0
Flue Outlet Terminal (75mm) C.17.2.26.00.0
Air Inlet Terminal (75mm) C.17.2.26.00.0
Sealed System Kit C.08.0.02.00.0
Stand Off Back Plate (Boiler only) C.08.0.03.00.0
Stand Off Back Plate (Boiler + Sealed System Kit) C.08.0.05.00.0

Installation & Servicing Instructions Page : 4

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

All dimensions in mm.

in mm

2. BOILER LOCATION

All dimensions in mm.

150

2.1 DIMENSIONS AND MINIMUM
CLEARANCES

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

2.2 SERVICE CONNECTIONS

Gas, water, air and flue pipe,
condensation, and electrical
connections are as shown. Gas :

0.5 inch BSP female. Flow/Return

0.75 inch BSP female.

An optional stand-off frame is
also available which mounts
behind the boiler to leave a
50mm deep space behind the
boiler. This is to permit pipe
routing behind the boiler if
required. See Section 1.5 -

Optional Accessories.

1

Figure 2.1.2
Dimensions

Air Intake

Flue

1

305 (W h en servicing appliance )
10 (W h en appliance is operating )

Figure 2.1.1

100

Minimum Clearances

2.3 POSITION

The Celsius 25 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

34

Air

162

Top View

408

Flue

34

21

27

210

140

Elec

270

Return

471

Base View

Flow

Condense

40

621

9

4

2

25

Gas

Service Connection Locations All dimensions are in mm.

Installation & Servicing Instructions Page : 5

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

Scotland, with respect to the installation of the boiler in a room or internal space containing
a bath or shower.
Where a room-sealed appliance is installed in a room containing a bath or shower, any
electrical switch or appliance control, utilising mains electricity, should be so situated that it
cannot be touched by a person using the bath or shower.
Compartment installation is permitted - such compartments must be constructed in
accordance with BS 6798.

Chimneys not used for
venting any other

appliance may be used.

Secure air & flue pipes at
chimney outlet.

[NB: Refer to
Section 2.8.3]

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

The Keston Celsius 25 can be located virtually anywhere desired provided that all
regulations are complied with. Because of the boiler's compact size and venting flexibility,
the installation is not limited to a boiler room setting. Before locating the boiler near a living
space consider whether the sounds generated by the boiler will be objectionable. The
boiler may be located within a cupboard enclosure to reduce noise levels if located within a

living space. LPG boilers must not be installed in a cellar.

2.4 ELECTRICAL

2.4.1 Electrical Connections

The boiler must be connected to a permanent 230V ~ 50Hz supply, fused at 3A.

An additional switched live supply 230V ~ 50Hz rated at 2A or a pair of volt
free contacts must be provided from the external system controls. Wiring

external to the boiler must be in accordance with current I.E.E wiring regulations
and local regulations.
The method of connection to the mains electricity supply must facilitate complete
electrical isolation of the boiler, preferably by the use of a fused, unswitched three
pin plug and a shuttered socket-outlet, both complying with the requirements of BS

1363. There must be only one common method of isolation for the boiler and its
control system.

Figure 2.3

Installation & Servicing Instructions Page : 6

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

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

The connection point to the mains supply should be readily accessible and
adjacent to the boiler, except for rooms containing a bath or a shower. Refer to
section 2.3 Position.

2.4.2 External Wiring & Controls

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

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

2.5 BOILER SIZE SELECTION

The Celsius 25 will automatically adjust heat output and pump speed to match the system
requirements at any given time. Efficiency and combustion levels are maintained at
optimum levels throughout the possible output range. The Celsius 25 is therefore suitable

for all systems with a total heat load within the maximum range of the boiler.

2.6 GAS SUPPLY

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

Minimum/Maximum Gas Pressure:

Natural gas pressure before the gas valve must be maintained at between 18 mbar (7.2 in
WG) and 22 mbar (8.8 in) while the boiler is running.
LPG pressure must be maintained between 31.5 mbar (12.4 in w.g) and 37.6 mbar (14.8
in w.g) while the boiler is running.
Gas pressures above or below these levels will lead to problems associated with the gas
valve's internal pressure regulator.

Supply pipes to the boiler must not be sized less than the boiler inlet connection
(15 mm). Due consideration must be given to the supply pressure to other gas
appliances in the premises. Reduction in dynamic gas supply pressure will result in
intermittent ignition failures. Ensure gas supply pipe work is adequately sized for
the length of run from the meter to the boiler at a supply rate of 26.1 kW.

A gas cock is supplied loose with the boiler. This cock should be fitted in the gas line to
the boiler as close to the boiler as possible so that it is easily identified as the cock to
isolate the boiler.

2.7 WATER SYSTEMS

All piping must be installed in accordance with all applicable local and Water Supply
Bylaws for forced hot water heating systems.
Consideration must be given to pipe capabilities and pressure drop through the piping.
Water treatment must be carried out to BS 7593 : Treatment of Water in Hot Water
Central Heating Systems.

a The Celsius 25 is suitable for use on open, vented water systems with combined

feed and vent fitted to the boiler return.

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

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

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

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

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

Water Authority.

e Always use a system complying with the requirements of BS 5449 and BS 6798.

Installation & Servicing Instructions Page : 7

Figure2.7.1 : Open Vented System Diagram

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

f System design must ensure an open circuit is always available to ensure

circulation when the pump overrun function is operating after boiler shutdown.

g Copper tubing to BS 2871 Part 1 or barrier plastic pipe suitable to 110OC, such as

Unipipe, is recommended.

h 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.

i 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

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

sited to allow complete draining of the system.

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

consulted as to the compatibility of the thermal store with a Keston Celsius 25.
Thermal store units where the boiler directly heats an open vented thermal store
are not suitable for use with the Celsius 25.

Expansion
Pipe

Celsius 25

Expansion
Tank

Minimum
9ft Height

28mm

Minimum

Safety
Valve

FLOW

RETURN

By-pass

Rad. 2 Rad. 1

Valve

Cylinder

L/S
Valve

Valve

2.7.1 Open Vented Systems

A typical system is shown in Figure 2.7.1 which includes a combined feed and
vent. Note that the combined feed and vent must be fitted to the primary
RETURN. A safety valve is specified for the primary flow to ensure discharge path
at all times in the event the feed/vent connection is isolated from the boiler
flow.[see 2.7.2(i)] Note that the minimum static head required is 9 ft at the top of
the boiler.
Although suitable for open vented systems with combined feed and vent
arrangements, the Celsius 25 is a low water content boiler. As such, any air
entrainment within the system water will produce boiler “kettling”. It is therefore

Installation & Servicing Instructions Page : 8

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

Drain

Cock

recommended, if in any doubt, to consider the use of sealed systems where
possible.

Air Vent

Hose
Union
bib tap

Celsius 25

Expansion

Vessel

Safety
Valve

Figure 2.7.2 : Sealed System Diagram

2.7.2 Sealed Systems

A sealed system kit option
(C.08.0.02.00.0) is available for
the Celsius 25 featuring 8 litre
expansion vessel, safety valve
and connection manifold housed
in a white casing which can be
fixed to the base of the boiler.
The kit also incorporates
isolating valves on the flow,
return and gas pipes. This allows
the system kit to also be used as
a pre-installation jig. The
illustration below shows the
dimensions of the kit.

By-pass
Bal.
Valve

L/S

HEATING CIRCUIT

Double Check
Valve

Test Cock

RETURN

FLOW

BS 1010:2
Stop Tap

SEALED SYSTEM
KIT DIMENSIONS

471mm

Hosepipe

( disconnected

after filling )

Hose
Connector

2

5

0

m

m

275mm

Sealed systems must be designed in accordance with BS 5449 and BS 7074 Pt1.
A typical sealed system is shown in Figure 2.7.2. It must include :

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

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

Installation & Servicing Instructions Page : 9

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

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

with the requirements of BS 5449 and BS 7074 Pt 1. The vessel must be

positioned on the primary return to the boiler.

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

local water authority requirements.

(v) There must be no permanent connection of mains water to the boiler

system.

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

110 oC.

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

2.7.3 Hot Water System (if applicable)

The hot water storage vessel must be of the indirect type (certain direct cylinders
can be used provided they are suitably adapted by fitting an immersion calorifier).
DIRECT CYLINDERS MUST NOT BE USED. Further guidance is provided in BS

1394. It is advisable to fit a locksheild valve on the cylinder return to enable
balancing of the flow rate through the cylinder.

The Keston Spa range of stainless steel unvented cylinders are an ideal
option for use with the Keston Celsius 25. The Keston Spa range combine
exceptional recovery times with durable, long life stainless steel
construction and all associated controls. Contact Keston Boilers Ltd for
information

2.7.4 Boiler By-pass Piping

Boiler water flows are critical to the operation of the boiler. If flow cannot be
maintained through the system piping to meet the minimums required by the
boiler, insufficient water flows through the boiler will cause the boiler to "kettle" or
even produce steam which can damage the heat exchanger and will invalidate the
heat exchanger warranty. In addition, an open circuit is required after boiler
shutdown to permit circulation during the boilers 2 minute pump overrun
sequence.
It is normally advisable to incorporate a boiler by-pass in the system, especially if
thermostatic radiator valves are used. The flow/return differential should be 10oC
to 15oC.

2.7.5 Air Elimination

In the initial charge of water to the boiler system and in all subsequent additions of
water to the system some air will be dissolved in the water. As the water is heated
the air is driven out of the solution and will collect in high spots in the system.

These air bubbles can interfere with pumping and heat transfer and must be
eliminated.

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

2.7.6 System Pump Selection (if required)
The Celsius 25 features an integral circulating pump which has sufficient excess
head to drive most domestic systems. The available head is c.5kPa (0.5m). If the
system index circuit resistance is in excess of the available head from the integral
pump an additional system pump will be required.

Installation & Servicing Instructions Page : 10

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

The schematic below illustrates a recommended approach to using an additional
system pump. The additional system pump should be sized to overcome the
index circuit resistance only as the boilers integral pump will overcome boiler
resistance.

Celsius
25

If an additional pump is required the selected pump must comply with BS 1394.

2.8 FLUE SYSTEM

2.8.1 Design

Individual air supply and flue outlet pipes are used. The material used for flue
outlet &/or air inlet must be muPVC to BS 5255 and/or BSEN1566-1 and
BSEN1329 of an internal diameter of 51 mm. (i.e. nominal 50 mm diameter
muPVC solvent weld waste pipe).

Alternatively, where flue or air intake lengths
of up tu 60m are required, Glynwed Friatec
DN70 pipe may be used.

Both 50mm flue outlet terminal and 50mm air
inlet terminal are supplied and are illustrated in
Figure 2.8.1. Both terminals are identical. The
flue and air terminals must be fitted to the
appropriate duct using solvent weld adhesive.
If 75mm terminals are required these can be
obtained from your Keston Boilers stockist.
Request part numbers C.17.2.26.00.0
(terminals) and C.17.2.00.60.0 (50 to 75
adapters).

Expansion
Vessel

Safety
Valve

Permanently

open by-pass

Additional system
pump.

Primary flow

Primary Return

Flue Outlet/Air Inlet Terminals

Figure 2.8.1 : Terminals

2.8.2 Maximum Lengths

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

50mm 75mm
Maximum Air Inlet Length : 39.0m 117.0m
Maximum Flue Outlet Length : 20.0m 60m
Maximum Total Flue and Air Intake Length : 40.0m 120.0m

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.
A 92.5o sweep elbow is equivalent to 1.0m straight length.

Example (assuming 50mm muPVC flue and air pipework)
Air inlet uses two one 92.5o sweep elbows. Hence, maximum length permissible
(i.e. a+b in figure 2.8.2) = 39.0m - 1.0m - 1.0m = 37.0m

Installation & Servicing Instructions Page : 11

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

Flue outlet uses one 92.5o sweep elbow. Hence, maximum length permissible (i.e.
c+d in figure 2.8.2 = 20.0m - 1.0 m = 19.0m

Figure 2.8.2 : Flue & Air Maximum Length Example

2.8.3 Slope

'Horizontal' flue outlet pipework MUST
slope at least 2 degrees (32 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 be prevented from
entering the pipe. There must be no

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

AIR

b

a

Celsius 25

FLUE

d

c

Figure 2.8.3 :

Flue Condensate Drain
Point Example

To Terminal

To Boiler

Tee Fitting

Due the low temperature of the flue
gases further condensate will form
within the flue system. Drain points,

6 in min.

with suitable traps, must therefore be
incorporated within the flue system at
the base of vertical flue sections in
excess of 8m, for 50mm muPVC pipe flue systems. These additional condensate
drains must be run to discharge as detailed in section 2.11. Such drain points can
be formed using standard muPVC fittings. Refer to the example in Figure 2.8.3.

2.8.4 Terminations

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

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

Installation & Servicing Instructions Page : 12

WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

Dimensions (mm)

Flue

Terminal

Air

Inlet

50300A Below or beside openable window, air brick,

etc.

7575B Below gutters, soil pipes, drain pipes.

50200C Below eaves.

50200D Below balconies or car port roof.

5075E From vertical drain or soil pipes.

50200F From internal or external corner.

100200G 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.

Table 2.8.4 Minimum Flue Terminations & Air Inlet Dimensions

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.
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.

The Keston Celsius 25, as with any condensing boiler, will generate a
condensate “plume” from the flue terminal in all weather conditions.
Consideration must therefore be given to the effect of this “plume” when
selecting a location for the flue terminal.

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

2.8.5 Clearances From Wall

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

2.8.6 Distance Between Flue Outlet & Air Inlet

There is no maximum - the terminations must not be on opposite sides of the
dwelling but can be in areas of unequal pressure..
A minimum clearance of at least 200 mm must be left between the terminations.

2.8.7 General Installations

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

Rubber collars are available for flue and air terminals to finish the external wall
face around the terminals (Part No C.08.0.00.07.0)

2.9 AIR SUPPLY

The Celsius 25 is a room sealed appliance and therefore does not require purpose
provided ventilation to the boiler room for combustion air.

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WD209/1/2000 Chapter 2 - Boiler Connections The Keston Celsius 25 & 25P

2.10 COMPARTMENT INSTALLATION

Due consideration should be given to BS5440 pt 1 with regard to compartment ventilation
requirements. High and low level ventilation is required for cooling purposes as follows:

Position of air vent Air from room Air direct from Outside
High 306 cm
Low 306 cm

Both vents must communicate to the same room or be on the same wall to outside.

2.11 CONDENSATE DRAINAGE

Being a condensing boiler, the Celsius 25 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 15 mm internal diameter within the
dwelling. Condensate should preferably be drained into the sanitary waste system or,
alternatively, the rainwater system of the property in most cases. Ensure in all cases that
the disposal of the condensate is in accordance with any local regulations in force.

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

The connection to the condensate drain of the boiler, and the condensate drain pipework
itself, should be properly sealed to ensure there is no possibility of leakage into the
dwelling.

2

2

153cm
153cm

2

2

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

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WD209/1/2000 Chapter 3 : Installation The Keston Celsius 25 & 25P

3. INSTALLATION OF THE BOILER

Read Chapter 2 - Boiler Location and decide upon the position of the boiler.

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

3.1 WALL MOUNTING BRACKET

a Place the bracket on

the wall horizontally
with the pre-drilled
holes at the bottom
and position as
dictated by the
template supplied
within the boiler
packaging.

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).

191

Figure 3.1 Wall Mounting Fixing Locations

All dimensions in mm.

3.2 MOUNTING THE BOILER

a Lift and locate the boiler in the studs protruding from the wall bracket.
b Fix the boiler on the bracket studs using the nuts supplied.

3.3 ASSEMBLY PRACTICE

Remove all plastic debris and burrs when installing air intake piping. Plastic filings caused
by cutting muPVC 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.

3.4 INSTALLING FLUE AND AIR PIPES

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

Remember the flue pipe must slope downwards back towards the boiler and this is best
achieved using 92.5o bends.

a Using the template supplied within the boiler packaging mark the positions of the

two holes for the flue and air pipes on the wall(s) or ceiling.

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

Installation & Servicing Instructions Page : 15

WD209/1/2000 Chapter 3 : Installation The Keston Celsius 25 & 25P

3.4.1 Diameter of holes.

i) Allowance must be made for socketed

lengths if these are to be passed through
the holes :

du = unsocketed = 56mm

ds = socketed = 65mm

ii) For 'horizontal' runs of flue pipe the holes

must either be oversized or cut at a 2
slope (the latter may be difficult on long
holes).

3.4.2 Oversizing

For every 1m length of run, L, the minimum
diameter of the horizontal hole, D, must be du +
32 mm or ds + 32 mm respectively, assuming the
pipe touches the wall at points T otherwise D will
have to be increased by clearance from T. See
Section 3.4.3 - Examples.

3.4.3 Examples

a. Wall Depth L = 750 mm

Unsocketed pipe du = 56 mm
Diameter hole D = 56+[750/1000 x 32]

b. Wall depth L = 2.3 m

Socketed Pipe ds = 65 mm
Diameter Hole D = 65+[2.3 x 32]

c. Measure, cut and check the air and flue pipes to pass to the exit from the

wall(s) or ceiling.

diameter

diameter

D

o

Flue Pipe

= 56+24
= 80 mm

= 65+73.5
= 138.5 mm

T

d

u

L

d

s

Always thoroughly deburr all pipes and, most important, remove shavings from
within the pipe.

d. Mount the boiler on the wall bracket and fix the flue and air spigots

(packed loose with the boiler and with appropriate gaskets) to the boiler
flue and air outlet connections (the flue spigot incorporates a combustion
test plug) tightly to ensure there is no leakage. Assemble, using adhesive,
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 3.5
Condensate Drainage).

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

pipework), cut and assemble the pipework.

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

System and make good all holes.

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

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

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WD209/1/2000 Chapter 3 : Installation The Keston Celsius 25 & 25P

h. Check all connections for security and re-seal any joints using solvent

cement where soundness may be in doubt.

Note: It is equally important to seal the air inlet with solvent cement as the flue outlet

pipe joints.

3.5 CONDENSATE DRAINAGE

Connect the condensate drainage system to the boiler. It is advisable to use a detachable
fitting at connection to the boiler to enable easy removal for servicing.
Fill the condensate trap by pouring water into the boiler flue spigot until water is seen to
flow freely from the condensate drainage system. Make the final connection of flue pipe to
the boiler.

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

3.6 WATER SYSTEM

Connect the flow and return pipework to the boiler. Details of system requirements are
given in Chapter 2 - Section 2.7 Water Systems.

Connections : 0.75” BSPF

For optimum performance after installation, this boiler and its associated central heating
system must be flushed in accordance with the guidelines given in BS7592:1992,
"Treatment of water in domestic hot water central heating systems".
This must involve the use of a proprietary cleaner, such as Fernox Superfloc, or
BetzDearborn's Sentinel X300 or X400. Full instructions are supplied with the products,
but for immediate information, please contact Fernox on 01799 550811 or BetzDearborn
on 0151 420 9563.
For long term protection against corrosion and scale, after flushing, it is recommended
that an inhibitor such a Fernox MB1 or BetzDearborn's Sentinel X100 is dosed in
accordance with the guidelines given in BS7593:1992.

3.7 GAS SUPPLY

Connect the gas supply to the appliance. Details of gas supply requirements are given in
Chapter 2 - Section 2.6 Gas Supply. Supply of adequate gas pressure (with the boiler
running) is critical to ensure reliable operation of the boiler.
Connections : 0.75 inch BSPF.

3.8 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 1.0mm2 to BS 6500 Table 16
(material code H05VV-F).

3. The permanent live supply connection may be via a 3 amp fused double pole
switch, serving only the boiler. (Refer to Chapter 2 - Section 2.4 Electrical Supply).
The system controls and 2A switched supply for the boiler must also be supplied
via this isolator.

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. Remove the factory fitted
link wire between terminals SL and SL(Link) on the boiler.
The supply cable(s) must be connected to the main terminals as follows:

Installation & Servicing Instructions Page : 17