Main Heating Main Heat 12 Supplement

7219628 - 01 (4/15)
United Kingdom
Main Heat 12 - 15 - 18 - 24 - 30
Condensing Central Heating Boiler
Installation & Service Manual
These instructions include the Benchmark Commissioning Checklist and should be left with the user for safe keeping.
page 1
Building Regulations and the Benchmark Commissioning Checklist
Building Regulations (England & Wales) require notification of the installation of a heating appliance to the relevant Local Authority Building Control
Department. From 1 April 2005 this can be achieved via a Competent Persons Self Certification Scheme as an option to notifying the Local Authority directly.
Similar arrangements will follow for Scotland and will apply in Northern Ireland from 1 January 2006.
The Health & Safety Executive operates the 'Gas Safe Register', a self-certification scheme for gas heating appliances.
These arrangements represent a change from the situation whereby compliance with Building Regulations was accepted as being demonstrated by
completion of the Benchmark Logbook (which was then left on site with the customer).
With the introduction of Self Certification Schemes, the Benchmark Logbook is being withdrawn. However, a similar document in the form of a commissioning
checklist and service interval record is incorporated at the back of these instructions.
This company is a member of the Benchmark initiative and fully supports the aims of the programme. Its aim is to improve the standards of installation and
commissioning of central heating systems in the UK and to encourage the regular servicing of all central heating systems to ensure safety and efficiency.
Building Regulations require that installations should comply with manufacturer's instructions. It is therefore important that the commissioning checklist is

completed by the installer. The relevant section of Building Regulations only relates to dwellings. Therefore the checklist only applies if the appliance is being
installed in a dwelling or some related structure.
The flowchart below gives guidance for installers on the process necessary to ensure compliance with Building Regulations.
Natural Gas
Main 12 Heat ErP
G.C.No 41-467-23
Main 15 Heat ErP
G.C.No 41-467-24
Main 18 Heat ErP
G.C.No 41-467-25
Main 24 Heat ErP
G.C.No 41-467-26
Main 30 Heat ErP
G.C.No 41-467-27
The Benchmark Scheme
Benchmark places responsibilities on both manufacturers and installers. The purpose is to ensure that customers are provided with the correct equipment for
their needs, that it is installed, commissioned and serviced in accordance with the manufacturer's instructions by competent persons and that it meets the
requirements of the appropriate Building Regulations. The Benchmark Checklist can be used to demonstrate compliance with Building Regulations and
should be provided to the customer for future reference.
Installers are required to carry out installation, commissioning and servicing work in accordance with the Benchmark Code of Practice which is available from
the Heating and Hotwater Industry Council who manage and promote the Scheme. Visit www.centralheating.co.uk for more information.
© Baxi Heating UK Ltd 2015 All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, or stored in any
retrieval system of any nature (including in any database), in each case whether electronic, mechanical, recording or otherwise, without the prior written
permission of the copyright owner, except for permitted fair dealing under Copyrights, Designs and Patents Act 1988.
Applications for the copyright owner's permission to reproduce or make other use of any part of this publication should be made, giving details of the
proposed use, to the following address:
The Company Secretary, Baxi Heating UK Ltd,
Brooks House, Coventry Road, Warwick. CV34 4 LL
Full acknowledgement of author and source must be given.
WARNING: Any person who does any unauthorised act in relation to a copyright work may be liable to criminal prosecution and civil claims for damages.
page 2
Installer Notification Guidelines

page 3
Legislation
This company declares that no substances harmful to health are contained in the appliance or used during appliance manufacture.
The appliance is suitable only for installation in GB and IE and should be installed in accordance with the rules in force, and only used in a
suitably ventilated location.
In GB, the installation must be carried out by a Gas Safe Registered Installer. It must be carried out in accordance with the relevant requirements of the:

Gas Safety (Installation & Use) Regulations.
The appropriate Building Regulations either The Building Regulations, The Building Regulations (Scotland), Building Regulations (Northern Ireland).
The Water Fittings Regulations or Water Byelaws in Scotland.
The Current I.E.E. Wiring Regulations.
Where no specific instructions are given, reference should be made to the relevant British Standard Code of Practice.
In IE, the installation must be carried out by a competent Person and installed in accordance with the current edition of I.S. 813 'Domestic Gas Installations',
the current Building Regulations and reference should be made to the current ETCI rules for electrical installation.
All systems must be thoroughly flushed and treated with inhibitor (see section 6.2).
Codes of Practice, most recent version should be used
In GB the following Codes of Practice apply:
Standard Scope
BS 6891 Gas Installation.
BS 5546 Installation of hot water supplies for domestic purposes.
BS EN 12828 Heating systems in buildings.
BS EN 12831 Heating systems in buildings - calculation of load.
BS EN 14336 Installation & commissioning of water based heating systems.
BS 6798 Installation of gas fired hot water boilers.
BS 5440 Part 1 Flues.
BS 5440 Part 2 Ventilation.
BS 7074 Expansion vessels and ancillary equipment for sealed water systems.
BS 7593 Treatment of water in domestic hot water central heating systems.
In IE the following Codes of Practice apply:
Standard Scope
I.S. 813 Domestic Gas Installations.
The following BS standards give valuable additional information;
BS 5546 Installation of hot water supplies for domestic purposes.
BS EN 12828 Heating systems in buildings.
BS EN 12831 Heating systems in buildings - calculation of load.
BS EN 14336 Installation & commissioning of water based heating systems.
BS 7074 Expansion vessels and ancillary equipment for sealed water systems.
BS 7593 Treatment of water in domestic hot water central heating systems.
IMPORTANT - Installation, Commissioning, Service & Repair
This appliance must be installed in accordance with the manufacturer's instructions and the regulations in force. Read the instructions fully before installing or
using the appliance.
In GB, this must be carried out by a competent person as stated in the Gas Safety (Installation & Use) Regulations.
Definition of competence: A person who works for a Gas Safe registered company and holding current certificates in the relevant ACS modules, is deemed
competent.
In IE, this must be carried out by a competent person as stated in I.S. 813 "Domestic Gas Installations"!.
NOTE: The addition of anything that may interfere with the normal operation of the appliance without express written permission from the manufacturer or his
agent could invalidate the appliance warranty. In GB this could also infringe the Gas Safety (Installation and Use) Regulations.
Warning - Check the information on the data plate is compatible with local supply conditions.
All Gas Safe registered engineers carry an ID card with their licence number and a photograph. You can check your engineer is registered by telephoning
0800 408 5500 or online at www.gassaferegister.co.uk
The boiler meets the requirements of Statutory Instrument "The Boiler (Efficiency) Regulations 1993 No 3083"!and is deemed to meet the requirements of
Directive 92/42/EEC on the energy efficiency requirements for new hot water boilers fired with liquid or gaseous fuels:-
Type test for purpose of Regulation 5 certified by:
Notified Body 0086.
Product/Production certified by:
Notified Body 0086.
For GB/IE only.
page 4
Safe Manual Handling
General
The following advice should be adhered to, from when first handling the boiler to the final stages of installation, and also during maintenance.
Most injuries as a result of inappropriate handling and lifting are to the back, but all other parts of the body are vulnerable, particularly shoulders, arms and

hands. Health & Safety is the responsibility of EVERYONE.
There is no 'safe' limit for one man - each person has different capabilities. The boiler should be handled and lifted by TWO PEOPLE.
Do not handle or lift unless you feel physically able.
Wear appropriate Personal Protection Equipment e.g. protective gloves, safety footwear etc.
Preparation
Co-ordinate movements - know where, and when, you are both going.
Minimise the number of times needed to move the boiler - plan ahead.
Always ensure when handling or lifting the route is clear and unobstructed. If possible avoid steps, wet or slippery surfaces, unlit areas etc. and take special
care on ladders/into lofts.
Technique
When handling or lifting always use safe techniques - keep your back straight, bend your knees. Don't twist - move your feet, avoid bending forwards and
sideways and keep the load as close to your body as possible.
Where possible transport the boiler using a sack truck or other suitable trolley.
Always grip the boiler firmly, and before lifting feel where the weight is concentrated to establish the centre of gravity, repositioning yourself as necessary.
See section 10.3 of these instructions for recommended lift points.
Remember
The circumstances of each installation are different. Always asses the risks associated with handling and lifting according to the individual conditions.
If at any time when installing the boiler you feel that you may have injured yourself STOP !!
DO NOT 'work through' the pain - you may cause further injury.
IF IN ANY DOUBT DO NOT HANDLE OR LIFT THE BOILER - OBTAIN ADVICE OR ASSISTANCE BEFORE PROCEEDING !!
page 5
Contents
1.0 Introduction
2.0 General Layout
3.0 Appliance Operation
4.0 Technical Data
5.0 Dimensions and Fixings
6.0 System Details
7.0 Site Requirements
8.0 Flue Options
9.0 Plume Displacement
10.0 Installation
11.0 Electrical
12.0 Commissioning the Boiler
13.0 Fitting the Outer Case
14.0 Servicing the Boiler
15.0 Changing Components
16.0 Short Parts List
17.0 Fault Finding
Benchmark Checklist
page 6
1.0 Introduction
1.1 Description
1. The Main Heat range are gas fired room sealed fan assisted condensing central heating boilers.
2. The maximum output of the Main Heat are:-
12 - 11.82 kW Pn (Non condensing)
12.81 kW Pnc (Condensing)
15 - 15.24 kW Pn (Non condensing)
16.49 kW Pnc (Condensing)
18 - 17.81 kW Pn (Non condensing)

19.27 kW Pnc (Condensing)
24 - 22.0 kW Pn (Non condensing)
23.8 kW Pnc (Condensing)
30 - 30.18 kW Pn (Non condensing)
32.61 kW Pnc (Condensing)
All boilers automatically adjust their outputs according to the system load.
NOTE: The maximum output of the 30 model is factory set at 22.0 kW (Pn).
This can be altered to 30.18 kW (Pn). See Section 10.8.
3. It is designed for use on Natural Gas (G20).
4. The boiler is suitable for fully pumped open vented central heating and domestic hot water systems and sealed systems.
5. A label giving details of the model, serial number and Gas Council number is situated on the rear of the lower door panel (Fig. 1).
6. The boiler data badge is positioned on the air box door (Fig. 2).
7. The boiler is intended to be installed in residential / domestic environments on a governed meter supply only.
8. The boiler must be installed with one of the purpose designed flues such as the standard horizontal flue kit, part no 236921.
Fig. 1
Fig. 2

Contents of Pack
The pack contains:-
Boiler
Wall Plate
Template & 'Quick Fit' Guide
Literature Pack
Fittings Pack
1.2 Important Information
Man-made mineral fibre
Some component parts of this appliance (insulation pads, gaskets and rope seals) are manufactured from man-made mineral fibre.
Prolonged or excessive exposure to this material may result in some irritation to the eyes, skin or respiratory tract.
It is advisable to wear gloves when handling these items.
Irritant dust will only be released from the items if they are broken up or subjected to severe abrasion. In these instances a suitable dust mask and
goggles should be worn.
Always thoroughly wash hands after installation, servicing or changing components.
When disposing of any items manufactured from man-made mineral fibre care must be exercised.
If any irritation of the eyes or severe irritation of the skin is experienced seek medical attention.
page 7
2.0 General Layout
2.1 Layout (Figs. 3,4,5& 6)
1. Wall Plate
2. Flue Elbow
3. Heat Exchanger
4. Burner
5. Air Box
6. Fan Protection Thermostat
7. Fan Assembly
8. Condensate Trap
9. PCB Housing Assembly
10. Gas Tap
11. Gas / Air Ratio Valve
12. Flow Pipe Connection
13. Return Pipe Connection
14. Flow Temperature Safety Thermostat - Black
15. Flow Temperature Thermistor - Red
16. Flow Switch (dry fire protection)

Fig. 3, Fig. 4, Fig. 5 & Fig. 6

page 8
3.0 Appliance Operation
3.1
1. Switched Live On: When the switched live switches on if the flow temperature is less than the set point then pump overrun occurs. When the
switched live switches on if the flow temperature is greater than the set point then pump overrun occurs.
2. Pump On: The pump is on while the fan, spark generator and gas valve are off. After 10 seconds if the flow switch has made then fan pre-purge
occurs. After 10 seconds if the flow switch has not made then anticycle occurs.
3. Fan Pre-Purge: The pump and fan are on while the spark generator and gas valve are off. After 5 seconds ignition occurs.
4. Ignition: The pump, fan, spark generator and gas valve are on. If a flame is detected then burner on occurs. If a flame is not detected within 5
seconds and less than 5 ignition attempts have been made then fan purge occurs. If a flame is not detected within 5 seconds and 5 ignition attempts
have been made then ignition lockout occurs.
5. Burner On: The pump, fan and gas valve are on while the spark generator is off. Flow temperature is controlled by varying the fan speed (and thereby
the gas rate) to achieve optimum operation. If the flow temperature is greater than the set point or the TRVs all shut down then fan post purge occurs.
6. Fan Post Purge: The pump and fan are on while the spark generator and gas valve are off. After 5 seconds if the TRVs are not shut down then pump
overrun occurs. After 5 seconds if the TRVs are shut down then anti-cycle occurs.
7. Pump Overrun: The pump is on while the fan, spark generator and gas valve are off. After 1 minute anticycle occurs.
8. Anti-cycle: The pump, fan, spark generator and gas valve are off. After 3 minutes if the flow temperature is less than the set point then pump on
occurs. After 3 minutes if the flow temperature is greater than the set point then pump overrun occurs.
9. Ignition Lockout: The pump, fan, spark generator and gas valve are off. The boiler can only be reset by manually using the reset button.

page 9
4.0 Technical Data
4.1 Main 12, 15, 18, 24, 30 Heat ErP
Appliance Type C13 C33 C53
Appliance Category CAT I 2H
Heat Input Qn Hs (Gross) Max Min
12 model kW 13.34 10.2
15 model kW 16.88 10.2
18 model kW 20.18 10.2
24 model kW 24.50 10.2
30 model
(see note) kW 33.76 10.2
Heat Output Pn (Gross)
(Non Condensing 70° C Mean Water Temp)
Max Min
12 model kW 11.82 9.14
15 model kW 15.24 9.14
18 model kW 17.81 9.14
24 model kW 22.00 9.14
30 model kW 30.18 9.14
Heat Output Pnc (Gross)
(Condensing 40°C Mean Water Temp)
Max Min
12 model kW 12.81
15 model kW 16.49 10.1
18 model kW 19.27
24 model kW 23.8 10.1
30 model kW 32.61 10.1
NOTE: The maximum output of the 30 model is factory set
at 22.0kW.
This can be altered to 30.18kW - see section 10.8.
Product Characteristic Database
(SEDBUK)
SAP 2009 Annual Efficiency
12 model - The efficiency is 88.7 %
15 model - The efficiency is 89.4 %
18 model - The efficiency is 88.7 %

24 model - The efficiency is 88.8 %
30 model - The efficiency is 88.8 %
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 has been
certified by 0086.
Max Gas Rate
(After 10 Mins) (2H - G20 - 20mbar)
(12) (15) (18) (24) (30)
m3/hr 1.34 1.64 1.94 2.31 2.95
ft3/hr 47.3 52.1 68.5 83.3 104.2
Injector (Natural Gas)
6.5mm Diameter
Nox Class 5
Horizontal
Flue Terminal
Dimensions
Diameter 110mm
Projection 150mm
Connections
Gas Supply - 1/2in
BSPT
Central Heating Flow - 22mm
Central Heating Return - 22mm
Condensate Drain - 1 in BSP
Outercase Dimensions
Overall Height Inc Flue Elbow - 750mm
Casing Height - 600mm
Casing Width - 390mm
Casing Depth - 280mm
Clearances
(For unventilated compartments see Section 7.2)
Both Sides 5mm Min
Above Casing 200mm
Min
Below Casing 50mm
Min
Front (For Servicing) 500mm
Min
Front (In Operation) 5mm Min
Weights kg
Packaged Boiler
Carton 36.2
Packaged Flue Kit 3.6
Installation Lift
Weight 26.0
CO/CO2Ratio Up to a maximum of 0.004
CO2Level 9% ± 1%
Electrical Supply 230V~ 50Hz
(Appliance must be connected to an earthed supply)
Power Consumption 80W
External Fuse Rating 3A
Internal Fuse Rating (BS 4265)
Fuse 3.15 AT (PCB)
Electrical Protection IPX2
Water Content
litres 2.6
pints 4.6
Static Head
max 30 metres
min 1 metre
Low Head 0.2m min
System Detail

fully pumped open vented & sealed systems
Gas Connection
G 1/2"!B.S.P. Thread
Controls
boiler thermostat, safety thermostat, flow switch, electronic
flame sensing, temperature protection thermostat &
condensate blockage sensor
Inlet Pressure at Gas Valve (Natural Gas)
Min 18.1 mbar
Max 22.5 mbar
(see Section 12.1)
Flow Temperature (adjustable)
55° C to 78° C (± 5° C)
Recommended System Temperature Drop
Condensing 20°C
NOTE: All data in this section are nominal values and subject to normal production tolerances
page 10@
4.2 Technical Parameters
Technical parameters for boiler space heaters
Main Heat ErP 12 15 18 24 30
Condensing boiler Yes Yes Yes Yes Yes
Low-temperature boiler(1) No No No No No
B1 boiler No No No No No
Cogeneration space heater No No No No No
Combination heater No No No No No
Rated heat output Prated kW 12 15 18 24 30
Useful heat output at rated heat output and high temperature regime P4kW 12.0 15.0 18.0 24.0 30.0
Useful heat output at 30% of rated heat output and low temperature regime(1) P1kW 3.8 4.8 5.9 7.8 9.7
Seasonal space heating energy efficiency ns%91 91 92 92 92
Useful efficiency at rated heat output and high temperature regime(2) n4%90.3 88.6 90.3 88.3 89.5
Useful efficiency at 30% of rated heat output and low temperature regime(1) n1%96.5 96.5 96.5 96.8 96.5
Auxiliary electricity consumption
Full load elmax kW 0.070 0.080 0.110 0.130 0.145
Part load elmin kW 0.007 0.007 0.007 0.007 0.007
Standby mode PSB kW 0 0 0 0 0
Other items
Standby heat loss Pstby kW 0.100 0.100 0.100 0.100 0.100

Ignition burner power consumption Pign kW - - - - -
Annual energy consumption QHE kWh
GJ
10550
38
13187
47
15652
56
20870
75
26087
94
Sound power level, indoors LWA dB 38 46 49 52 58
Emissions of nitrogen oxides NOXmg/kWh 20 20 20 19 24
(1) Low temperature means for condensing boilers 30°C, for low temperature boilers 37°C and for other heaters 50°C return temperature (at heater inlet).
(2) High temperature regime means 60°C return temperature at heater inlet and 80°C feed temperature at heater outlet.
See
The back cover for contact details.
page 11
5.0 Dimensions and Fixings
DIMENSIONS
A600mm
B280mm
C390mm
D150mm Ø Min.
E162.5mm
F96mm
Fig. 7

The 1.5° fall provided by the elbow is to allow condensate to run back to the boiler, for disposal through the condensate discharge pipe.
Fig. 8
SIDE FLUE (left and right)
For every 1m of horizontal flue length, the clearance above the top of the flue
elbow should be 27.5mm to incorporate the 1.5° fall in the flue from the terminal
to the elbow.
Flue length (Y) Clearance (X)
up to 1m
1m - 2m
2m - 3m
27.5mm
55mm
82.5mm
page 12
6.0 System Details
6.1 Water Circulating Systems
1. The appliance is suitable for use with open vent fully pumped systems and sealed systems.
The following conditions should be observed on all systems:
The static head must not exceed 30m of water.
The boiler must not be used with a direct cylinder.
Drain cocks should be fitted to all system low points.
All gas and water pipes and electrical wiring must be installed in a way which would not restrict the servicing of the boiler.
Position isolating valves as close to circulating pump as possible.
It is recommended that the return pipe is fitted with an automatic air vent as close to the boiler as is practical.
6.2 Treatment of Water Circulating Systems
1. All recirculatory water systems will be subject to corrosion unless they are flushed and an appropriate water treatment is applied. To prevent this,
follow the guidelines given in BS 7593 "Treatment of Water in Domestic Hot Water Central Heating Systems"!and the treatment manufacturers
instructions.
2. Treatment must involve the use of a proprietary cleanser, such as Sentinel X300 or X400, or Fernox F3 and an inhibitor such as Sentinel X100 or
Fernox MB-1.
3. Full instructions are supplied with the products, for further information contact Sentinel (0800 389 4670) or Fernox (0870 870 0362).
Failure to flush and add inhibitor to the system will invalidate the appliance warranty.
4. It is important to check the inhibitor concentration after installation, system modification and at every service in accordance with the inhibitor
manufacturer's instructions. (Test kits are available from inhibitor stockists.)
5. For information or advice regarding any of the above contact Technical Enquiries 0844 871 1555.
page 13
6.3 Pipework
1. The sizes of flow and return pipes from the boiler should be determined by normal methods, according to the requirements of the system. The
connections on the boiler are 22mm.
2. A 20°C drop in temperature across the system is recommended for condensing boilers. Existing radiators may be oversized and so allow this, but
where radiator sizing is marginal it may be advisable to retain a system temperature drop of 11°C.
NOTE: On 30 models 28mm pipe should be used to connect to the boiler flow and return.
3. In systems using non-metallic pipework it is necessary to use copper pipe for the boiler Flow and Return. The copper must extend at least 1 metre

from the boiler and include any branches (Fig. 9).
Fig. 9
Fig. 10
6.4 Low Head Installation
1. Using a close couple arrangement the minimum head is as shown in the diagrams (Figs. 10 & 11) subject to the following conditions:
a) The pump being adjusted to give a 20°C drop across the boiler.
b) The pump must be fitted on the flow.
c) The pump must be fitted in accordance with the pump manufacturer's instructions.
d) The open vent pipe must be taken up from a tee in a horizontal section of the flow pipe.
An alternative Low Head Installation (Fig. 12)
2. For heads below 400mm then a combined vent and feed pipe may be connected. This must be a minimum of 22mm diameter. It is recommended that
an air separator is fitted when using a combined feed and vent pipe.
Fig. 11

Fig. 12
6.5 Pump
1. Providing that the cold feed and open vent pipe are positioned correctly (e.g. the system is not prone to pumping over, air entrainment etc.) the pump
may be fitted on the primary return pipe.
page 14
6.6 System Controls
This boiler does not require a bypass.
This boiler does not require a permanent live.
The pump only needs wiring directly to the boiler for fully TRV'd systems.
1. To comply with Part L1 of the Building Regulations the heating system into which the boiler is installed should include the following:
a) zone controls
b) timing controls
c) boiler control interlocks
2. Such a system needs to be fully pumped and must provide independent temperature and time control to both the heating and hot water circuits and
have a boiler interlock.
3. The boiler should be controlled so that it operates on demand only. Where it is proposed to effect control by thermostatic radiator valves, a room
thermostat (or other device such as a flow switch - a flow switch is integral to this boiler) should also be provided to switch off the boiler when there is
no demand for heating or hot water.
4. The interlock for the CH circuit can be provided by either a Room Thermostat or a fully TRV'd system with the pump wired back to the boiler without a
bypass. Connection diagrams for both options for Y and S plan systems are shown.
Y Plan, Room Thermostat System, CH Interlocked By Room Thermostat
At least the Radiator(s) near the Room Thermostat not TRV'd Pump run from Switched Live
By-pass permitted but not required for Part L1 compliance

S Plan, Room Thermostat System, CH Interlocked By Room Thermostat
At least the Radiator(s) near the Room Thermostat not TRV'd
Pump run from Switched Live By-pass permitted but not required for Part L1 compliance
Y Plan, Fully TRV'd System, CH Interlocked By Boiler Flow Switch
Room Thermostat should not be fitted
Pump must be run from Boiler P/F connection for Part L1 compliance
By-pass not permitted (must be valved off) for Part L1 compliance
S Plan, Fully TRV'd System, CH Interlocked By Boiler Flow Switch
Room Thermostat should not be fitted
Pump must be run from Boiler P/F connection for Part L1 compliance
By-pass not permitted (must be valved off) for Part L1 compliance

page 15
6.7 Sealed Systems (Fig. 13)
1. SAFETY VALVE - A safety valve complying with the requirements of BS 6750 Part 1 must be fitted close to the boiler on the flow pipe by means of a
horizontal or vertically upward connection with no intervening valve or restrictions and should be positioned to facilitate testing. The valve should be
pre-set and non-adjustable to operate at a pressure of 3 bar. It must be arranged to discharge any water or steam through a pipe to a safe outlet
position.
2. PRESSURE GAUGE - A pressure gauge of minimum range 0-4 bar with a fill pressure indicator must be fitted to the system, preferably at the same
point as the expansion vessel in an easily visible position.
3. EXPANSION VESSEL - An expansion vessel complying with the requirements of BS 4814 must be fitted to the system by means of a connection
close to the inlet side of the circulating pump in accordance with the manufacturers instructions, the connecting pipe being unrestricted and not less
than 15mm (1/2in) nominal size. The volume of the vessel should be suitable for the system water content and the nitrogen or air charge pressure
should not be less than the system static head (See Table. 1).
Further details of sealed system design can be obtained from BS 5449 and the British Gas publication entitled 'Specifications for Domestic Wet Central
Heating Systems'.
4. FILLING POINT - A filling point connection on the central heating return pipework must be provided to facilitate initial filling and pressurising and also
any subsequent water loss replacement / refilling. The sealed primary circuits may be filled or replenished by means of a temporary connection
between the primary circuit and a supply pipe provided a 'Listed' double check valve or some other no less effective backflow prevention device is
permanently connected at the inlet to the circuit and the temporary connection is removed after use. The filling method adopted must be in accordance
with all relevant water supply regulations and use approved equipment.
Your attention is drawn to,
for GB: Guidance G24.2 and recommendation R24.2 of the Water Regulations Guide.
for IE: the current edition of I.S. 813 "Domestic Gas Installations"!.
5. MAKE UP SYSTEM - A method of replacing water lost from the system should be provided either by means of a make up vessel of not more than 3
litres capacity, mounted above the highest point of the system, or by re-pressurisation of the system.
6. VENTING - A method of venting the system during filling and commissioning must be provided by fitting automatic air vents or by venting manually.
7. HOT WATER STORAGE - The hot water storage vessel must be of the indirect coil type. All components used in the system must be suitable for
operation at 110°C and at the pressure allowed by the safety valve.
Fig. 13
Method of determining minimum valve of expansion vessel volume for sealed systems using Main Boilers
Vessel Charge
Pressure (Bar)
Initial System
Pressure (Bar)
Multiply Total
Water Content Of
System By (Litres)
0.5
0.5
1.0
1.5
2.0
0.067
0.112
0.207
0.441
1.0
1.0
1.5
2.0
0.087
0.152
0.330
1.5 1.5
2.0
0.125
0.265
Example :- System Volume = 75 litres
Vessel Charge Pressure = 1.0 bar
Initial System Pressure = 1.5 bar
Then :- 75 x 0.152 = 11.4 litres
Expansion Vessel Volume
Table. 1

NOTE Where a vessel of the calculated size is not obtainable then the next available larger size should be used.
Fig. 14
page 16
7.0 Site Requirements
7.1 Location
NOTE: Due to the high efficiency of the boiler a plume of water vapour will be discharged from the flue.
This should be taken into account when siting the flue terminal.
1. The boiler may be fitted to any suitable wall with the flue passing through an outside wall or roof and discharging to atmosphere in a position permitting
satisfactory removal of combustion products and providing an adequate air supply. The boiler should be fitted within the building unless otherwise
protected by a suitable enclosure i.e. garage or outhouse. (The boiler may be fitted inside a cupboard - see Section 7.2).
2. If the boiler is sited in an unheated enclosure then it is recommended to incorporate an appropriate device for frost protection in the system controls.
3. If the boiler is fitted in a room containing a bath or shower it MUST NOT BE fitted in zone 0, 1 or 2, ONLY within the shaded area (Figs. A & Bshows
zone dimensions for a bathtub. For other examples refer to the Current I.E.E. Wiring Regulations) reference must be made to the relevant
requirements.
In GB this is the current I.E.E. Wiring Regulations and Building Regulations.
In IE reference should be made to the current edition of I.S. 813 "Domestic Gas Installations"!and the current ETCI rules.
4. If the boiler is to be fitted into a building of timber frame construction then reference must be made to the current edition of Institute of Gas Engineers
Publication IGE/UP/7 (Gas Installations in Timber Framed Housing).
Fig. A
7.2 Ventilation of Compartments
1. Where the boiler is installed in a cupboard or compartment, no air vents are required for cooling purposes providing that the minimum dimensions
below are maintained.
Sides 15mm
Top 200mm
Bottom 50mm
Front 30mm
2. If the boiler is installed in a smaller cupboard or compartment it must be ventilated according to BS 5440 Part 2 and the minimum clearances given in
section 4.0 "Technical Data"!maintained.

3. Any compartment should be large enough to house the boiler only.
NOTE: The ventilation label on the front of the outer case MUST NOT BE REMOVED when the appliance is installed in a compartment or
cupboard.
Fig. B
page 17
7.3 Clearances (Figs. 15 &16)
1. A flat vertical area is required for the installation of the boiler.
2. These dimensions include the necessary clearances around the boiler for case removal, spanner access and air movement. Additional clearances
may be required for the passage of pipes around local obstructions such as joists running parallel to the front face of the boiler.
3. For unventilated compartments see Section 7.2.
Fig. 15