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Benchmark Logbook is being withdrawn.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.