Baxi Duo-tec Combi 24 HE A Installation and maintenance instructions

Installation & Service Instructions Combi 24 HE
This is a Wall Mounted Powered Flue Condensing Combination Boiler Gas Fired
Central Heating Unit.
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 Body 0086.
For use in GB/IE only.
These instructions include the Benchmark Commissioning Checklist and should be
left with the User for safe keeping.

2
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Benchmark Logbook is being withdrawn.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.
CONTENTS
Legislation 4
1.0 Introduction 5
2.0 General Layout 6
3.0 Appliance Operation 7
4.0 Technical Data 8
5.0 Dimensions and Fixings 9
6.0 System Details 10
7.0 Site Requirements 13
8.0 Installation 19
9.0 Commissioning 24
10.0 Completion 26
11.0 Servicing the Boiler 27
12.0 Changing Components 29
13.0 Electrical 39
14.0 Short Parts List 40
15.0 Fault Finding 41
Benchmark Checklist 46
Section Page
Natural Gas
Main Combi 24 HE
G.C.No47 474 02

3
INSTALLER NOTIFICATION GUIDELINES
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

LEGISLATION
4
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”.
Lifting - This product should be lifted and handled by two people. Stooping
should be avoided and protective equipment worn where necessary.
Carrying & lifting equipment should be used as required, e.g. when installing
in a loft space.
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
Main 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 6.2).
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.

5
1.0 INTRODUCTION
1.1 Description
1. The Main Combi 24 HE is a fully automatic gas
fired wall mounted condensing combination boiler. It
is room sealed and fan assisted, and will provide
central heating and mains fed domestic hot water.
2. The boiler is set to give a maximum output of
25.2 kW (condensing).
3. It is designed for use on Natural Gas (G20) and can
be converted to use Propane.
4. The boiler is suitable for use only on fully pumped
sealed heating systems. Priority is given to domestic
hot water.
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. 5111073.
8. All systems must be thoroughly flushed and
treated with inhibitor (see section 6.2).
1.2 Optional Extras
1. Various flue extensions, bends, vertical flue kits,
control accessories etc. are available as optional
extras. These are detailed in a separate publication.
Data Badge
Fig. 1
Control Box
Case Front Panel

2.0 GENERAL LAYOUT
6
2.1 Layout
1. Air Pressure Switch
2. Expansion Vessel
3. Burner Manifold
4. Automatic Air Vent
5. DHW Plate Heat Exchanger
6. Circulation Pump
7. Drain Off Point
8. Pressure Relief Valve
9. Optional Integral Timer Position
10. Central Heating System Pressure Gauge
11. Control PCB
12. Control Box
13. 3-Way Valve Assembly
14. Condensate Trap
15. Flame Sensing Electrode
16. Spark Electrode
17. Burner
18. Primary Heat Exchanger
19. Fan Assembly
20. Secondary Heat Exchanger
21. On / Off / Reset Selector Switch
22. Burner & Fault Indicator Neon
23. Power Neon
24. Flame Failure & Fault Indicator Neon
25. Central Heating Temperature Control
26. Hot Water Temperature Control
19
18
17
14
15
16
13
12 11
10 9
21 22 23 24 25 26 10 9
7
6
3
4
5
8
2
1
2
1
0
4
3
bar
Reset Burner On
Flame Failure
Power On
Fig. 2
Fig. 3
20

7
3.0 APPLIANCE OPERATION
NOTE: All delay timers mentioned in 3.1 and 3.2
are overridden by domestic hot water demand.
3.1 Central Heating Mode (Fig. 4)
1. With a demand for heating, the pump circulates
water through the primary circuit. At a pre-
determined flow rate the central heating flow 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.
3.2 Domestic Hot Water Mode (Fig. 5)
1. Priority is given to the domestic hot water supply.
A demand at a tap or shower will override any central
heating requirement.
2. The flow of water will operate the DHW flow switch
which causes the 3 way valve to change position.
This will allow the pump to circulate the primary water
through the DHW plate heat exchanger.
3. The burner will light automatically and the
temperature of the domestic hot water is controlled
by the temperature sensor.
4. When the domestic hot water demand ceases the
burner will extinguish and the diverter valve will
remain in the domestic hot water mode, unless there
is a demand for central heating.
IMPORTANT: When the selector switch is in the
‘0’ (Off) position the electrical supply to the boiler
is isolated. The boiler will not operate and the
integral timer (if fitted) will require resetting once
the selector switch is turned to either the DHW
or CH position.
1
2
4
5 6
7
8
9
10
11
1213141516
17
18
19
20
21
22
23
24
25
26
3
1 Primary Heat Exchanger
2 Burner
3 Ignition Electrode
4 Flame Sensing Electrode
5 Gas Valve
6 Pump
7 Automatic Air Vent
8 Plate Heat Exchanger
9 Flow Sensor with Filter
10 Pressure Relief Valve
11 Boiler Drain Point
12 Heating Return
13 Cold Water Inlet On/Off Valve and Filter
14 Gas Inlet
15 Domestic Hot Water Outlet
16 Heating Flow
17 Pressure Gauge
18 Hydraulic Differential Pressure Sensor Microswitch
19 Automatic By-Pass
20 Hydraulic Differential Pressure Sensor
21 Diverter Valve Assembly
22 Domestic Hot Water Flow Priority Assembly
23 Domestic Hot Water Flow Priority Microswitch
24 Temperature Sensor
25 Overheat Thermostat
26 Expansion Vessel
27 Secondary Heat Exchanger
Key
Central Heating Circuit
Domestic Hot Water Circuit
Fig. 4
Fig. 5
1
2
4
5 6
7
8
9
10
11
1213141516
17
18
19
20
21
22
23
24
25
26
3
27
27

4.0 TECHNICAL DATA
8
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
Temperatures
C.H. Flow Temp (adjustable)
35°C to 85°C max (± 5°C)
D.H.W. Flow Temp
35°C to 65°C max (± 5°C)
dependent upon flow rate
Heat Input CH
Max Min
kW 24.8 10.6
Heat Output CH (Non-Condensing)
Max Min
kW 24 9.8
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
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 ± 0.2
Appliance Type C12 C32
Heat Output CH (Condensing)
Max Min
kW 25.2 10.1
Heat Input DHW
Max
kW 24.8
Heat Output DHW
Max
kW 24
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 5 mm Min
R.H. Side 5 mm Min (In Operation)
20 mm 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 50
Installation Lift Weight 43.5
Connections copper tails
Gas Supply - 22mm
Central Heating Flow - 22mm
Central Heating Return - 22mm
Cold Water Mains Inlet - 15mm
DHW Flow - 15mm
Pressure Relief Discharge - 15mm
NOxClass 3
Electrical Protection IPX4D
Condensate Drain 1” BSP
LPG Propane - G31
Burner Injector 15 x 0.77mm diameter
Burner Pressure
Propane mbar
Inlet Pressures
mbar
Max Rate
21.8 ± 0.5
Min Rate
4.4 ± 0.2
37
Central Heating Primary Circuit
Pressures
bar
Safety Discharge 3
Max Operating 2.5
Min Operating 0.5
Recommend Operating 1-2
DHW Circuit bar
Pressures
Max Operating 8
Min Operating 0.2
Min Operating Pressure
at 11.1 l/min 0.9
Flow Rates l/min
DHW Flow Rate
@ 30°C Rise 11.5
DHW Flow Rate
@ 35°C Rise 9.8
Min Working
DHW Flow Rate 2.5
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 1.0
of Boiler (unpressurised)
Max Gas Rate (Natural Gas - G20)
(After 10 mins)
m3/h 2.62

9
5.0 DIMENSIONS AND FIXINGS
Dimensions
A780mm
B345mm
C450mm
D116mm Ø Min.
E185mm
F190mm
G131mm
65mm 65mm 65mm 65mm
View from under the appliance
Gas Inlet
Heating
Flow
Domestic Hot
Water Outlet
Cold Water
Inlet
Heating
Return
130mm
165.7mm
95mm
Left Hand Side
of Boiler
Fig. 7
360° Orientation
Tube Ø 100mm
DC
B
A
E
G
F
Fig. 6
68mm
265mm
Condensate
Drain

6.0 SYSTEM DETAILS
10
6.1 Information
1. The Main Combi 24 HE Condensing Combination
Boiler is a ‘Water Byelaws Scheme - Approved
Product’. To comply with the Water Byelaws your
attention is drawn to the following installation
requirements and notes (IRN).
a) IRN 001 - See text of entry for installation
requirements and notes.
b) IRN 302 - Byelaw 14.
2. Reference to the WRc publications, ‘Water fittings and
materials directory’ and ‘Water supply byelaws guide’
give full details of byelaws and the IRNs.
6.2 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 be suitable for aluminium and
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.
6.3 Bypass
1. The boiler is fitted with an automatic integral
bypass.
6.4 System Control
1. The boiler is designed for use in a heating system
that incorporates external controls, i.e. a minimum of
a timer device.
2. An integral electro-mechanical or electronic timer is
available as an optional extra.
3. For optimum operating conditions and maximum
economy the fitting of a programmable thermostat is
recommended.

11
6.0 SYSTEM DETAILS
6.5 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. There are connection points on the mains cold
water inlet and central heating return isolating taps to
which the optional filling loop kit (Part No. 248221)
can be assembled.
3. The filling method adopted must be in accordance
with all relevant water supply regulations and use
approved equipment.
4. 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. 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.
6.6 Expansion Vessel
(Central Heating only)
1. The appliance expansion vessel is pre-charged to
0.5 bar. Therefore, the minimum cold fill pressure is
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”.
6.7 Pressure Relief Valve (Fig. 9)
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 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. 8
Fig. 9
Stop
Valve
Double
Check
Valve
DHW
Mains
Inlet
CH
Return
Temporary
Hose
Pressure Relief Valve
Discharge Pipe
Stop
Valve

6.0 SYSTEM DETAILS
12
6.8 Domestic Hot Water Circuit
1. All DHW circuits, connections, fittings, etc. should
be fully in accordance with relevant standards and
water supply regulations.
2. Your attention is drawn to:
for GB: Guidance G17 to G24 and recommendation
R17 to R24 of the Water Regulations Guide.
for IE: the current edition of I.S. 813 “Domestic Gas
Installations”.
3. A single check valve must be fitted as shown in
Fig. 10 to prevent backflow to the supply pipe and to
ensure the efficient operation of the expansion vessel
which is required to accommodate the thermal
expansion of the water.
4. When the domestic water system includes any
device which prevents water expanding back
towards the supply (check valve, loose jumpered
stopcock, water meter, water treatment device) then
an expansion vessel must be fitted (eg. Zilmet 160ml,
R1/215bar).
5. If the hot water expansion is not provided for, then
high pressures can develop which may result in
damage to fittings and devices on the system.
6. The boiler’s maximum working mains pressure is 8
bar, therefore all pipework, connections, fittings, etc.
should be suitable for pressures in excess of 8 bar. A
pressure reducing valve must be fitted for pressures
in excess of 8 bar. The manufacturer of any outlet
fittings, such as a shower valve, may require a lower
maximum pressure. The pressure reduction must
take account of all fittings connected to the DHW
system.
6.9 Showers
1. If a shower control is supplied from the appliance
it should be of the thermostatic or pressure balanced
type. Thermostatic type shower valves provide the
best comfort and guard against water at too high a
temperature. Existing controls may not be suitable -
refer to the shower valve manufacturer.
6.10 Hard Water Areas
1. If the area of the installation is recognised as a
HARD WATER AREA then a suitable device should
be fitted to treat the mains water supply to the boiler.
Contact your Water Distribution Company for advice
on suitable devices.
Boiler
Other Tap
Outlets
Expansion
Vessel
To Hot
Taps
Check
Valve
Pressure
Reducing Valve
Stop Tap
Fig. 10

13
7.0 SITE REQUIREMENTS
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 that frost protection is incorporated
in the control system.
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 (Fig. 11 & 12)
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 alteration in
the area of installation.
2
1
0
4
3
bar
Reset Burner On
Flame Failure
Power On
200mm Min
780mm
450mm
200mm Min
20mm/5mm Min
see *NOTE:
5mm Min
5mm Min
450mm Min
For Servicing
Purposes
Fig. 11
Fig. 12
In Operation

7.0 SITE REQUIREMENTS
14
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. 13).
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 is 230V ~ 50Hz 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.
Fig. 13
Gas Service Cock

15
7.0 SITE REQUIREMENTS
7.6 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. Any pipe fitted externally must not exceed 3 metres.
7. Any condensate discharge pipework external to the
building (or in an unheated part of it e.g. garage) must
be insulated to protect against frost. It is also
recommended that the pipe diameter is increased to
32mm.
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
External termination to a drain or gully
Boiler
500mm min
2.5° Minimum fall
External 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

7.0 SITE REQUIREMENTS
16
7.7 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.
Terminal Position with Minimum Distance (Fig. 14) (mm)
A* Directly below an openable window, air vent or any other
ventilation opening. 300
B Below gutters, drain/soil pipe. 25
C Below eaves. 25
D Below balcony/car port roof. 25
E From vertical drain pipes and soil pipes. 25
F From internal or external corners. 25
G Above adjacent ground or balcony level. 300
H From a surface or boundary facing the terminal. 600
I Facing terminals. 1200
J For opening (door/window) in car port into dwelling. 1200
K Vertically from a terminal on the same wall. 1500
L Horizontally from a terminal on the same wall. 300
M* Above an opening, air brick, opening window etc. 300
N* Horizontally to an opening, air brick, opening window etc.
300
* In addition, the terminal should be no nearer than 150mm 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.
Fig. 14
L
G
G
E
J
D
K
G
AAD
F
H,I
B,C
F
Likely flue positions requiring
a flue terminal guard
M
N
300 min
Terminal
Assembly
Top View Rear Flue
Property Boundary Line
Fig. 15

17
7.0 SITE REQUIREMENTS
Fig. 17
Fig. 16
7.8 Flue Dimensions
The standard horizontal flue kit allows for flue lengths
between 100mm and 685mm from elbow to terminal
(Fig. 16).
The maximum permissible flue length is: 4 metres.
7.9 Flue Trim
1. The rubber flue trim supplied may be fitted to either
the outside wall or on the inner wall of installation.
7.10 Terminal Guard (Fig. 17)
1. When codes of practice dictate the use of terminal
guards, they can be obtained from most Plumbers’ and
Builders’ Merchants.
2. There must be a clearance of at least 50mm
between any part of the terminal and the guard.
3. When ordering a terminal guard, quote the appliance
name and model number.
4. The flue terminal guard should be positioned
centrally over the terminal and fixed as illustrated.
100mm 685mm

7.0 SITE REQUIREMENTS
18
7.11 Flue Options
1. The Main Combi 24 HE can be fitted with flue
systems as illustrated.
2. The standard flue is suitable only for horizontal
applications.
3. Maximum permissible equivalent flue lengths
are:-
Horizontal Concentric 4 metres
Vertical Concentric 4 metres
Vertical Twin Pipe 12 metres
4. Any additional “in line” bends in the flue system
must be taken into consideration.
Their equivalent lengths are:-
Concentric Pipes:
45° bend 0.5 metres
93° bend 1.0 metres
Twin Flue Pipe
45° 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
5. The illustrations opposite show examples of
maximum equivalent lengths.
6. Instructions for guidance and fitting are included
in each kit, where appropriate.
NOTE: Flue length is measured from point A to B
as shown.
Horizontal
Flues
Vertical
Flues
Vertical
Flues
(Twin Pipe)
B
A
B
A
B
A

19
8.0 INSTALLATION
8.1 Initial Preparation
The gas supply, gas type and pressure must be
checked for suitability before connection (see
Section 7.4).
1. After considering the site requirements
(see Section 7.0) position the fixing template on the
wall ensuring it is level both horizontally and
vertically.
2. Mark the position of the two most suitable fixing
slots for the wall plate and boiler lower fixing holes.
It is preferable to use the horizontal fixing slots. For
side flue exit, mark as shown (Fig. 18).
3. Mark the position of the centre of the flue hole
(rear exit). For side flue exit, mark as shown.
4. If required, mark the position of the gas and water
pipes. Remove the template.
5. Cut the hole for the flue (minimum diameter
116mm).
6. Drill the wall as previously marked to accept the
wall plugs supplied. Secure the wall plate using two
of the fixing screws.
7. Using a spirit level ensure that the plate is level
before finally tightening the screws.
8.2 Flushing
1. Connect a tube to the central heating flow or
return pipe (Fig. 19).
2. Flush thoroughly (see System Details, Section
6.2).
8.3 Preparing The Boiler
1. Remove all packaging.
2. Stand the boiler on its base by using the rear
lower edge as a pivot.
NOTE: A small amount of water may drain from
the boiler in the upright position.
Fig. 18
Fig. 19
190mm
For Side Flue Exit
Central Heating Return
Flushing Tube

8.0 INSTALLATION
20
8.4 Fitting The Boiler
1. Lift the boiler using the lower edges. Engage the
slots at the top rear of the boiler on the wall plate
hooks (Fig. 20).
2. Ensure that the boiler is level and sits against the
wall.
3. Take the two steel washers and remaining screws.
Using the previously drilled and plugged holes,
secure the bottom of the boiler to the wall (Fig. 21).
4. Remove the elbows, valves and sealing washers
from the packaging. The 3/4 in valve with internal
filter must be fitted to the central heating return. The
filter is visible through the branch connection of the
valve.
5. Using the sealing washers provided connect the
valves to the heating flow and return, and the cold
water inlet.
6. Connect the elbows to the gas service cock and
hot water outlet pipe, and then connect the elbows
to the boiler. Connect the elbows with flared ends to
the valves.
7. Ensure that the sealing washers are used on all
connections. The rubber washers must be used on
the gas connections.
8. The gas and water supplies, central heating flow
and return and domestic hot water flow can now be
connected.
8.5 Fitting the Pressure Relief
Discharge Pipe (Fig. 22)
1. Remove the discharge pipe from the kit.
2. Determine the routing of the discharge pipe in the
vicinity of the boiler. Make up as much of the
pipework as is practical, including the discharge pipe
supplied.
3. The pipework must be at least 15mm diameter
and run continuously downwards to a discharge
point outside the building. See section 6.7 for further
details.
4. Using one of the sealing washers, connect the
discharge pipe to the adaptor and tighten the nut.
5. Complete the discharge pipework and route it to
the outside discharge point.
IMPORTANT: Make all soldered joints before
connecting to the pressure relief valve.
Fig. 22
Fig. 20
Fig. 21
Pressure Relief Valve
Securing Screw
Washer
Wall Plate
Discharge Pipe