Benchmark MAIN Installation and maintenance instructions

© Baxi Heating UK Ltd 2007
Installation & Service Instructions System HE
Range
These instructions include the Benchmark Commissioning Checklist
and should be left with the user for safe keeping.

2© Baxi Heating UK Ltd 2007
Natural Gas
Main System 18 HE
G.C.No41 467 01
Main System 24 HE
G.C.No41 467 02
Main System 28 HE
G.C.No41 467 03
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.
CORGI operate 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Benchmark Logbook is being withdrawn.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 opposite gives guidance for installers on the
process necessary to ensure compliance with Building
Regulations.
The code of practice for the installation,
commissioning & servicing of central
heating systems.
“Main” supports
Baxi Heating UK Ltd is a
BS-EN ISO 9001 Accredited Company
© Baxi Heating UK Ltd 2007 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, Pentagon House,
Sir Frank Whittle Road, Derby, DE21 4XA.
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.

3
Installer Notification Guidelines
© Baxi Heating UK Ltd 2007
Choose Building
Regulations Notification
Route
Contact your relevant Local
Authority Building Control
(LABC) who will arrange
an inspection or contact
a government approved
inspector
LABC will record the data
and will issue a
certificate of compliance
CORGI will record the data and
will send a certificate of
compliance to the property
You must ensure that the
notification number issued by
CORGI is written onto the
Benchmark Checklist
Scheme Members only
Call CORGI on: 0870 88 88 777
or log onto:
www.corgi-notify.com
within 10 days
If you notify via CORGI Scheme,
CORGI will then notify the
relevant Local Authority
Building Control Scheme
on member's behalf
Complete the
Benchmark Checklist
Install and Commission this
appliance to manufacturer's
instructions
Competent Person's
Self Certification Scheme
Building Control
Complete the
Benchmark Checklist
Install and Commission this
appliance to manufacturer's
instructions

4
Legislation
© Baxi Heating UK Ltd 2007
Codes of Practice, most recent version should be used
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 CORGI 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”.
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 CORGI registered installers carry a CORGI identification card and have a
registration number. You can check your installer is registered by telephoning 0870
4012300 or writing to:-
1 Elmwood,
Chineham Business Park,
Crockford Lane,
Basingstoke. RG24 8WG
or check online at www.corgi-gas-safety.com
This company declare 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 CORGI
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 6.1).
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 5449 Forced circulation hot water 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 5449 Forced circulation hot water systems.
BS 7074 Expansion vessels and ancillary equipment
for sealed water systems.
BS 7593 Treatment of water in domestic hot water
central heating systems.
The boiler meets the requirements of Statutory Instrument “ The Boiler (Efficiency)
Regulations 1993 No3083” 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 0051.
Product/Production certified by:
Notified Bodies 0051.
For GB/IE only.

5
Safe Manual Handling
© Baxi Heating UK Ltd 2007
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 the ‘Installation’ section 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 !!

6© Baxi Heating UK Ltd 2007
CONTENTS
1.0 Introduction 7
2.0 General Layout 8
3.0 Appliance Operation 9
4.0 Technical Data 10
5.0 Dimensions and Fixings 13
6.0 System Details 14
7.0 Site Requirements 16
8.0 Flue Options 20
9.0 Plume Displacement 25
10.0 Installation 29
11.0 Commissioning 34
12.0 Completion 36
13.0 Servicing 37
14.0 Changing Components 39
15.0 Electrical 48
16.0 Short Parts List 49
17.0 Fault Finding 50
Benchmark Checklist 54
Section Page

7
1.0 Introduction
© Baxi Heating UK Ltd 2007
1.1 Description
1. The Main System HE range are fully automatic gas fired
wall mounted system boilers. They are room sealed and fan
assisted.
2. The boilers are set to give a maximum output of
18.9kW, 25.2kW or 29.3kW when in condensing mode.
3. They are designed for use on Natural Gas (G20) and can
be converted to use Propane.
4. The boiler incorporates a circulating pump and expansion
vessel. It is suitable for use only on fully pumped sealed
systems.
5. The boiler data badge gives details of the model, serial
number and Gas Council number and is situated on the
control box. It is visible when the case front panel is
removed (Fig. 1).
6. The boiler is intended to be installed in residential /
commercial / light industrial E.M.C. environments on a
governed meter supply only.
7. The boiler must be installed with one of the purpose
designed flues such as the standard horizontal flue kit, part
no. 5118489.
8. All systems must be thoroughly flushed and treated with
inhibitor (see section 6.1).
NOTE: There are several detail differences between
each model. Generally these do not affect the installation
or maintenance of the boiler, unless otherwise stated.
1.2 Contents of Pack
The pack contains:-
Boiler
Wall Plate (including taps)
Set of Pipe Connections
Template
Literature Pack
Data Badge
Fig. 1
Control Box
Case Front Panel

8
2.0 General Layout
© Baxi Heating UK Ltd 2007
2.1 Layout
1. Air Pressure Switch
2. Expansion Vessel
3. Burner Manifold
4. Automatic Air Vent
5. Circulation Pump
6. Drain Off Point
7. Pressure Relief Valve
8. System Pressure Gauge
9. PCB
10. Control Box
11. Condensate Trap
12. Flame Sensing Electrode
13. Spark Electrode
14. Burner
15. Primary Heat Exchanger
16. Fan Assembly
17. Secondary Heat Exchanger
18. On/Off/Reset Selector Switch
19. Temperature Control
20. Flame Failure or Blocked Condensate Drain
21. Safety Thermostat Activated (Boiler or Flue)
22. Fault on Fan or Flue
23. Fault on Pump or Low System Pressure
24. Fault on Temperature Sensor
25. Fault on Temperature Sensor
26. Power On
27. Boiler On
28. Burner On
When neons 20 to 25 are constantly illuminated, they
indicate the temperature of the central heating water.
16
15
14
11
12
13
10 9
8
18 19 8
6
5
3
4
7
2
1
2
1
0
4
3
bar
30°40°50°60°70°80°
Reset
30°40°50°60°70°80°
20 21 22 23 25
26 27 28
24
17

9
3.0 Appliance Operation
© Baxi Heating UK Ltd 2007
3.1 Operating Mode (Fig. 2)
1. With a demand for heating, the pump circulates water
through the primary circuit. At a pre-determined flow rate
the hydraulic differential pressure switch operates, initiating
the ignition sequence.
2. The main burner ignites at low rate, then the gas valve
controls the gas rate to maintain the heating temperature
measured by the temperature sensor.
3. When the flow temperature exceeds the setting
temperature, a 3 minute delay occurs before the burner
relights automatically (anti-cycling). The pump continues to
run during this period.
4. When the demand is satisfied the burner is extinguished
and the pump continues to run for a period of 3 minutes
(Pump Overrun).
IMPORTANT: When the selector switch is in the ‘0’
(Off) position the electrical supply to the boiler is
isolated. The boiler will not operate.
3.2 Frost Protection Mode
1. The frost protection mode is integral to the appliance and
functions when the selector switch (see Section 2.1) is in the
ON position ( ). If the system temperature falls below
5° C then the boiler will fire on its minimum setting until a
flow temperature of 30° C is reached. Further protection
can be incorporated by using a system frost thermostat.
3.3 Pump Protection
1. With the selector switch (see Section 2.1) in the ON
position ( ) the pump will automatically operate for 1
minute in every 24 hours to prevent sticking.
1
2
4
5 6
7
8
19
18
9
10 1211
14
13
15
16
17
3
Key
1 Heat Exchanger
2 Burner
3 Ignition Electrode
4 Flame Sensing Electrode
5 Gas Valve
6 Pump
7 Automatic Air Vent
8 Pressure Relief Valve
9 Boiler Drain Point
10 Gas Inlet
11 Boiler Flow
12 Boiler Return
13 Pressure Gauge
14 Automatic By-Pass
15 Hydraulic Differential Pressure Sensor
16 Safety Thermostat
17 Temperature Sensor
18 Expansion Vessel
19 Temperature Sensor
20 Secondary Heat Exchanger
Boiler Primary Circuit
Fig. 2
20

10
4.0 Technical Data
© Baxi Heating UK Ltd 2007
4.1 System 18 HE
Flue Terminal Diameter 100mm
Dimensions Projection 125mm
Outercase Dimensions
Casing Height - 780mm
Overall Height Inc Flue
Elbow - 965mm
Casing Width - 450mm
Casing Depth - 345mm
Clearances
Above Casing 200 mm Min
Below Casing 200 mm Min
Front 450 mm Min (For Servicing)
Front 5 mm Min (In Operation)
L.H. Side 5mm Min
R.H. Side 5mm Min (In Operation)
20mm Min (See Note*)
*NOTE: The boiler can be operated with a
clearance of 5mm at the right. This is also
sufficient for routine maintenance. However a
clearance of 20mm is required if it is necessary to
remove the secondary heat exchanger. This
should be considered when siting the appliance
and in the event of any subsequent alterations in
the area of installation
Weights kg
Packaged Boiler Carton 49
Installation Lift Weight 38.5
Central Heating Primary Circuit
Pressures
bar
Safety Discharge 3
Max Operating 2.5
Min Operating 0.5
Recommend Operating 1-2
Pump
Available Head See graph below
Expansion Vessel - (For Central Heating
only. Integral with appliance)
bar
Min Pre-charge Pressure 0.5
litre
Max Capacity of
CH System 125
Primary Water Content
of Boiler (unpressurised) 1.2
Connections copper tails
Gas Supply - 22mm
Central Heating Flow - 22mm
Central Heating Return - 22mm
Pressure Relief Discharge - 15mm
Temperatures
Flow Temp (adjustable)
35°C to 85°C max (± 5°C)
Heat Input
Max Min
kW 18.7 10.6
Electrical Supply 230V~ 50Hz
(Appliance must be connected to an
earthed supply)
Power Consumption 140W
External Fuse Rating 3A
Internal Fuse Rating
Fuse 2A Fast Blow to BS 4265
Appliance Category CAT II 2H 3P
Max Gas Rate (Natural Gas - G20)
(After 10 Mins)
m3/h 1.98
Inlet Pressure (Natural Gas - G20)
mbar 20
Burner Injector (Natural Gas - G20)
12 x 1.18mm Diameter
Burner Pressure (Natural Gas - G20)
Max Rate Min Rate
mbar 8.6 ± 0.5 3 ± 0.5
Appliance Type C12 C32 C52 NOxClass 3
Electrical Protection
IPX5D
Heat Output (Non-Condensing)
Max Min
kW 18 9.9
Heat Output (Condensing)
Max Min
kW 18.9 10.2
Condensate Drain 1” BSP
0
200 400 600 800 1000 1200
0.5
1
1.5
2
2.5
3
3.5
4
Metre (wg)
Flow Rate (l/h)
Pump - Available Head
0
5
4.5
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 0051.
SEDBUK Declaration For System 18 HE
The seasonal efficiency (SEDBUK) is 87.4% (87.3% LPG)
Band B
LPG Propane - G31
Burner Injector 0.77mm diameter
Burner Pressure
Propane mbar
Inlet Pressure
mbar
Max Rate
20 ± 0.5
Min Rate
6.6 ± 0.2
37

11
4.0 Technical Data
© Baxi Heating UK Ltd 2007
4.2 System 24 HE
Flue Terminal Diameter 100mm
Dimensions Projection 125mm
Outercase Dimensions
Casing Height - 780mm
Overall Height Inc Flue
Elbow - 965mm
Casing Width - 450mm
Casing Depth - 345mm
Clearances
Above Casing 200 mm Min
Below Casing 200 mm Min
Front 450 mm Min (For Servicing)
Front 5 mm Min (In Operation)
L.H. Side 5mm Min
R.H. Side 5mm Min (In Operation)
20mm Min (See Note*)
*NOTE: The boiler can be operated with a
clearance of 5mm at the right. This is also
sufficient for routine maintenance. However a
clearance of 20mm is required if it is necessary to
remove the secondary heat exchanger. This
should be considered when siting the appliance
and in the event of any subsequent alterations in
the area of installation
Weights kg
Packaged Boiler Carton 51
Installation Lift Weight 40.5
Central Heating Primary Circuit
Pressures
bar
Safety Discharge 3
Max Operating 2.5
Min Operating 0.5
Recommend Operating 1-2
Pump
Available Head See graph below
Expansion Vessel - (For Central Heating
only. Integral with appliance)
bar
Min Pre-charge Pressure 0.5
litre
Max Capacity of
CH System 125
Primary Water Content
of Boiler (unpressurised) 1.2
Connections copper tails
Gas Supply - 22mm
Central Heating Flow - 22mm
Central Heating Return - 22mm
Pressure Relief Discharge - 15mm
Temperatures
Flow Temp (adjustable)
35°C to 85°C max (± 5°C)
Heat Input
Max Min
kW 24.8 10.6
Electrical Supply 230V~ 50Hz
(Appliance must be connected to an
earthed supply)
Power Consumption 170W
External Fuse Rating 3A
Internal Fuse Rating
Fuse 2A Fast Blow to BS 4265
Appliance Category CAT II 2H 3P
Max Gas Rate (Natural Gas - G20)
(After 10 Mins)
m3/h 2.62
Inlet Pressure (Natural Gas - G20)
mbar 20
Burner Injector (Natural Gas - G20)
15 x 1.18mm Diameter
Burner Pressure (Natural Gas - G20)
Max Rate Min Rate
mbar 10.2 ± 0.5 2 ± 0.5
Appliance Type C12 C32 C52 NOxClass 3
Electrical Protection
IPX5D
Heat Output (Non-Condensing)
Max Min
kW 24 9.8
Heat Output (Condensing)
Max Min
kW 25.2 10.1
Condensate Drain 1” BSP
0
200 400 600 800 1000 1200
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Metre wg
l/h
Pump - Available Head
0
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 0051.
SEDBUK Declaration For System 24 HE
The seasonal efficiency (SEDBUK) is 87.4% (87.2% LPG)
Band B
LPG Propane - G31
Burner Injector 0.77mm diameter
Burner Pressure
Propane mbar
Inlet Pressure
mbar
Max Rate
21.8 ± 0.5
Min Rate
4.4 ± 0.2
37

12
4.0 Technical Data
© Baxi Heating UK Ltd 2007
4.3 System 28 HE
Flue Terminal Diameter 100mm
Dimensions Projection 125mm
Outercase Dimensions
Casing Height - 780mm
Overall Height Inc Flue
Elbow - 965mm
Casing Width - 450mm
Casing Depth - 345mm
Clearances
Above Casing 200 mm Min
Below Casing 200 mm Min
Front 450 mm Min (For Servicing)
Front 5 mm Min (In Operation)
L.H. Side 5mm Min
R.H. Side 5mm Min (In Operation)
20mm Min (See Note*)
*NOTE: The boiler can be operated with a
clearance of 5mm at the right. This is also
sufficient for routine maintenance. However a
clearance of 20mm is required if it is necessary to
remove the secondary heat exchanger. This
should be considered when siting the appliance
and in the event of any subsequent alterations in
the area of installation
Weights kg
Packaged Boiler Carton 51
Installation Lift Weight 40.5
Central Heating Primary Circuit
Pressures
bar
Safety Discharge 3
Max Operating 2.5
Min Operating 0.5
Recommend Operating 1-2
Pump
Available Head See graph below
Expansion Vessel - (For Central Heating
only. Integral with appliance)
bar
Min Pre-charge Pressure 0.5
litre
Max Capacity of
CH System 125
Primary Water Content
of Boiler (unpressurised) 1.2
Connections copper tails
Gas Supply - 22mm
Central Heating Flow - 22mm
Central Heating Return - 22mm
Pressure Relief Discharge - 15mm
Temperatures
Flow Temp (adjustable)
35°C to 85°C max (± 5°C)
Heat Input
Max Min
kW 28.9 11.9
Electrical Supply 230V~ 50Hz
(Appliance must be connected to an
earthed supply)
Power Consumption 180W
External Fuse Rating 3A
Internal Fuse Rating
Fuse 2A Fast Blow to BS 4265
Appliance Category CAT II 2H 3P
Max Gas Rate (Natural Gas - G20)
(After 10 Mins)
m3/h 3.06
Inlet Pressure (Natural Gas - G20)
mbar 20
Burner Injector (Natural Gas - G20)
15 x 1.25mm Diameter
Burner Pressure (Natural Gas - G20)
Max Rate Min Rate
mbar 10.9 ± 0.5 2.1 ± 0.5
Appliance Type C12 C32 C52 NOxClass 3
Electrical Protection
IPX5D
Heat Output (Non-Condensing)
Max Min
kW 28 11
Heat Output (Condensing)
Max Min
kW 29.3 11.3
Condensate Drain 1” BSP
0
200 400 600 800 1000 1200
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Metre wg
l/h
Pump - Available Head
0
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 0051.
SEDBUK Declaration For System 28 HE
The seasonal efficiency (SEDBUK) is 87.3% (87.2% LPG)
Band B
LPG Propane - G31
Burner Injector 0.77mm diameter
Burner Pressure
Propane mbar
Inlet Pressure
mbar
Max Rate
29.4 ± 0.5
Min Rate
5.2 ± 0.2
37

13
5.0 Dimensions and Fixings
© Baxi Heating UK Ltd 2007
Dimensions
A780mm
B345mm
C450mm
D107mm Ø Min.
E185mm
F190mm
G131mm
Heating
Return
(22mm)
Heating
Flow
(22mm)
Pressure Relief
Valve
(15mm)
Gas
Inlet
(22mm)
130 mm 130 mm 65 mm
Tap Rail
360° Orientation
Tube Ø 100mm
DC
B
A
E
G
F
At Least 1.5°
28mm
Condensate
Drain

14
6.0 System Details
© Baxi Heating UK Ltd 2007
6.1 Central Heating Circuit
1. The appliance is suitable for fully pumped SEALED
SYSTEMS ONLY.
Treatment of Water Circulating Systems
• All recirculatory water systems will be subject to corrosion
unless an appropriate water treatment is applied. This means
that the efficiency of the system will deteriorate as corrosion
sludge accumulates within the system, risking damage to pump
and valves, boiler noise and circulation problems.
• When fitting new systems flux will be evident within the
system, which can lead to damage of system components.
• All systems must be thoroughly drained and flushed out.
Using, for example Betz-Dearborn Sentinel X300 or X400 or
Fernox Superfloc Universal Cleanser. They should be used
following the flushing agent manufacturer’s instructions.
• System additives - corrosion inhibitors and flushing
agents/descalers should comply to BS7593 requirements, e.g.
Betz-Dearborn Sentinel X100 and Fernox-Copal which should
be used following the inhibitor manufacturer’s instructions.
Failure to flush and add inhibitor to the system will
invalidate the appliance warranty.
• It is important to check the inhibitor concentration after
installation, system modification and at every service in
accordance with the manufacturer’s instructions. (Test kits are
available from inhibitor stockists.)
• For information or advice regarding any of the above contact
Technical Enquiries.
6.2 Bypass
1. The boiler is fitted with an automatic integral bypass.
6.3 System Control
1. For optimum operating conditions, the heating system into
which the boiler is installed should include a control system.
2. Such a system will comprise of a timer control and separate
room or cylinder thermostats as appropriate.
3. The boiler should be controlled so that it operates on
demand only.
4. Operation of the system under control of the boiler
thermostat & TRV’s only does not produce the best results.

15
6.0 System Detail
© Baxi Heating UK Ltd 2007
6.4 System Filling and Pressurising
1. 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.
2. The filling method adopted must be in accordance with
all relevant water supply regulations and use approved
equipment.
3. 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”.
4. The sealed primary circuits may be filled or replenished
by means of a temporary connection between the 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.
6.5 Expansion Vessel
1. The appliance expansion vessel is pre-charged to 0.5 bar.
The vessel is suitable for correct operation for system
capacities up to 125 litres. For greater system capacities an
additional expansion vessel must be fitted. for GB refer to
BS 7074 Pt 1. For IE, the current edition of I.S. 813
“Domestic Gas Installations”.
6.6 Pressure Relief Valve (Fig. 4)
1. The pressure relief valve is set at 3 bar, therefore all
pipework, fittings, etc. should be suitable for pressures in
excess of 3 bar.
2. The pressure relief discharge pipe should be not less than
15mm dia, run continuously downward, and discharge
outside the building, preferably over a drain. It should be
routed in such a manner that no hazard occurs to
occupants or causes damage to wiring or electrical
components. The end of the pipe should terminate facing
down and towards the wall.
3. The discharge must not be above a window, entrance or
other public access. Consideration must be given to the
possibility that boiling water/steam could discharge from the
pipe.
Fig. 3
Fig. 4
Stop
Valve
Double
Check
Valve
Mains
Cold
Water
CH
Return
Temporary
Hose
Pressure Relief Valve
Discharge Pipe
Stop
Valve

16
7.0 Site Requirement
© Baxi Heating UK Ltd 2007
7.1 Location
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 7.3).
2. If the boiler is sited in an unheated enclosure then it is
recommended to leave the On/Off/Reset Selector Switch in
the On Position.
3. If the boiler is fitted in a room containing a bath or shower
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).
7.2 Clearances (Figs. 5 & 6)
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.
*NOTE: The boiler can be operated with a clearance of
5mm at the right. This is also sufficient for routine
maintenance. However a clearance of 20mm is required
if it is necessary to remove the secondary heat
exchanger. This should be considered when siting the
appliance and in the event of any subsequent alterations
in the area of installation.
200mm Min
780mm
450mm
200mm Min
20mm/5mm Min
see *NOTE:
5mm Min
5mm Min
450mm Min
For Servicing
Purposes
Fig. 5
Fig. 6
In Operation

17
7.0 Site Requirement
© Baxi Heating UK Ltd 2007
7.3 Ventilation of Compartments
1. Where the appliance is installed in a cupboard or
compartment, no air vents are required.
2. BS 5440: Part 2 refers to room sealed appliances
installed in compartments. The appliance will run
sufficiently cool without ventilation.
7.4 Gas Supply
1. The gas installation should be in accordance with the
relevant standards. In GB this is BS 6891. In IE this is the
current edition of I.S. 813 “Domestic Gas Installations”.
2. The connection to the appliance is a 22mm copper tail
located at the rear of the gas service cock (Fig. 7).
3. Ensure that the pipework from the meter to the
appliance is of adequate size. Do not use pipes of a smaller
diameter than the boiler gas connection (22mm).
7.5 Electrical Supply
1. External wiring must be correctly earthed, polarised and
in accordance with relevant regulations/rules. In GB this is
the current I.E.E. Wiring Regulations. In IE reference should
be made to the current edition of ETCI rules.
2. The mains supply must be 230V ~ 50Hzand fused at
3A maximum.
NOTE: The method of connection to the electricity
supply must facilitate complete electrical isolation of the
appliance.
Connection may be via a fused double-pole isolator
with a contact separation of at least 3mm in all poles
and servicing the boiler and system controls only.
3. When the system includes an indirect domestic hot
water cylinder it is recommended that a cylinder
thermostat is used in conjunction with a 3 port 2 position
valve or 2 port zone valve.
7.6 Bath & Shower Rooms
1. If the boiler is fitted in a room containing a bath or
shower, it can be fitted in zone 2, (Figs. A & B shows zone
dimensions for a bathtub. For other examples refer to
Section 601 of 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.
Fig. 7
Gas Service Cock
Zone 2
Zone 1
Zone 0
Zone 2
Zone 3
Zone 3
Zone 2
Window
Recess
Window
Recess
0.6 m 2.4 m
Ceiling
Outside
Zones
Outside Zones
Zone 3
Zone 3
Zone 2
Zone 2
Zone 1
Zone 0
2.25 m
Zone 2
Window
Recess
3.0 m
2.4 m
0.6 m
Fig. A
Fig. B
In GB Only
In GB Only

18
7.0 Site Requirement
© Baxi Heating UK Ltd 2007
7.7 Condensate Drain
FAILURE TO INSTALL THE CONDENSATE DISCHARGE
PIPEWORK CORRECTLY WILL AFFECT THE RELIABLE
OPERATION OF THE BOILER
The condensate discharge pipe MUST NOT RISE at any point
along its length. There MUST be a fall of AT LEAST 2.5° (50mm
per metre) along the entire run.
1. The condensate outlet terminates in a 1” BSP nut and seal
for the connection of 21.5mm (3/4in) plastic overflow pipe
which should generally discharge internally into the household
drainage system. If this is not possible, discharge into an outside
drain is acceptable.
2. Ensure the discharge of condensate complies with any
national or local regulations in force.
BS 6798:2000 & Part H1 of the Building Regulations give
further guidance.
3. The discharge pipe should be run in a proprietary drain pipe
material e.g. PVC, PVC-U, ABS, PVC-C or PP.
4. Metal pipework is NOT suitable for use in condensate
discharge systems.
5. The pipe should be a minimum of 21.5mm diameter and
must be supported using suitably spaced clips to prevent
sagging.
6. It is advisable to keep the condensate pipe internal.
7. External runs greater than 3 metres or runs in cold areas
should use 32mm waste pipe.
8. If the boiler is fitted in an unheated location the entire
condensate discharge pipe should be treated as an external run.
9. In all cases discharge pipe must be installed to aid disposal of
the condensate. To reduce the risk of condensate being
trapped, as few bends and fittings as possible should be used.
10. When discharging condensate into a soil stack or waste
pipe the effects of existing plumbing must be considered. If soil
pipes or waste pipes are subjected to internal pressure
fluctuations when WC's are flushed or sinks emptied then back-
pressure may force water out of the boiler trap and cause
appliance lockout.
Examples are shown of the following methods of termination:-
i) to an internal soil & vent pipe
ii) via an internal discharge branch (e.g. sink waste)
iii) to a drain or gully
iv) to a purpose made soakaway
Boiler
2.5° Minimum fall
Termination to an internal soil and
vent pipe
450mm min
Boiler
2.5° Minimum fall
External termination via internal discharge
branch
e.g sink waste - downstream
Sink
Pipe must terminate
above water level but
below surrounding
surface
Boiler Pipe must terminate above
water level but below
surrounding surface
2.5° Minimum fall
Termination to a drain or gully
Boiler
500mm min
2.5° Minimum fall
Termination to a purpose made soak-
away
Holes in the soak-away must
face away from the building
50mm per metre of pipe run
50mm per metre of pipe run
50mm per metre of pipe run
50mm per metre of pipe run

19
7.0 Site Requirement
© Baxi Heating UK Ltd 2007
7.8 Flue
NOTE: Due to the nature 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 following guidelines indicate the general requirements
for siting balanced flue terminals. For GB recommendations
are given in BS 5440 Pt 1. For IE recommendations are given
in the current edition of I.S. 813 “Domestic Gas
Installations”.
2. If the terminal discharges onto a pathway or passageway,
check that combustion products will not cause a nuisance
and that the terminal will not obstruct the passageway.
3. If a terminal is less than 2 metres above a balcony, above
ground or above a flat roof to which people have access,
then a suitable terminal guard must be provided.
IMPORTANT:
• Only ONE 25mm clearance is allowed per installation.
• Under car ports we recommend the use of the plume
displacement kit.
• The terminal position must ensure the safe and
nuisance - free dispersal of combustion products.
N
I
I
G
F
M
I
AAF
H
J,K
D
E
H
Likely flue positions requiring
a flue terminal guard
C
RA
I
J,K
I
L
S
B
T
U
Fig. 9
Fig. 8
300 min
Terminal
Assembly
Top View Rear Flue
Property Boundary Line
NOTE: The distance from a fanned draught appliance terminal
installed parallel to a boundary may not be less than 300mm in
accordance with the diagram below
Terminal Position with Minimum Distance (Fig. 9) (mm)
AaDirectly below an opening, air brick, opening
windows, etc. 300
BaAbove an opening, air brick, opening window etc. 300
CaHorizontally to an opening, air brick, opening window etc. 300
D Below gutters, soil pipes or drain pipes. 25
E Below eaves. 25
F Below balconies or car port roof. 25
G From a vertical drain pipe or soil pipe. 25
H From an internal or external corner. 25
I Above ground, roof or balcony level. 300
J From a surface or boundary line facing a terminal. 600
K From a terminal facing a terminal (Horizontal flue). 1200
From a terminal facing a terminal (Vertical flue). 600
L From an opening in carport (e.g. door, window)
into the dwelling. 1200
M Vertically from a terminal on the same wall. 1500
N Horizontally from a terminal on the same wall. 300
R From adjacent wall to flue (vertical only). 300
S From an adjacent opening window (vertical only). 1000
T Adjacent to windows or openings on pitched and flat roofs 600
U Below windows or openings on pitched roofs 2000
aIn addition, the terminal should be no nearer than 150 mm to an
opening in the building fabric formed for the purpose of accommodating
a built-in element such as a window frame. See BS 5440 Pt. 1.
*
Opening Window
or Door
100mm
MIN.
IMPORTANT: If fitting a Plume
Displacement Flue Kit, the air inlet
must be a minimum of 100mm from
any opening windows or doors (see
Section 9.0).
Plume
Displacement Kit
Air Inlet
Fig. 10

20
8.0 Flue Options
© Baxi Heating UK Ltd 2007
8.1 Horizontal Flue Systems
1. The Main System HE can be fitted with either
horizontal, vertical or twin flue systems as illustrated.
2. The standard flue is suitable only for horizontal
applications.
3. Maximum permissible equivalent flue lengths are:-
Horizontal Concentric (18 model) 5m
(24 model) 4m
(28 model) 3m
4. Any additional “in line” bends in the flue system must
be taken into consideration. Their equivalent lengths
are:-
Concentric Pipes:
135° bend 0.5 metres
93° bend 1.0 metres
Twin Flue Pipe
135° bend 0.25 metres
91.5° bend 0.50 metres
The elbow supplied with the standard horizontal flue is
not included in any equivalent length calculations
6. The illustrations opposite show examples of
maximum equivalent lengths.
NOTE: Flue length is measured from point X to Y
as shown.
Horizontal
Flues
Y
X
Plume Displacement Kit 60 /100 Ø
1M Extensions, 45° & 93° bends are
also available - see Section 9.0
NOTE: Horizontal flue pipes should always be installed with at least a 1.5° fall
from the terminal to allow condensate to run back to the boiler.
Y
X
This bend is equivalent to
1 metre
Total equivalent length (upto 3m) =
A+B+C+2x90°Bends
B
AC
This bend is equivalent to
1 metre