Baxi Duo-tec 2 Combi GA Range Installation & Servicing Instructions Manual

Gas fired wall mounted condensing combination boiler

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User's operating instructions & important warranty information (12 pages)

Technical manual (36 pages)

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Ian Bishop

May 12, 2025

Hi Guys, we have a problem where our combi duotec 2 28 ga keeps not heating the tap water, heating the radiators seems fone, but tap water heats very occasionally

1 comments:

Mr. Anderson

May 20, 2025

The Baxi Combi GA Range may not heat tap water consistently due to the following possible causes:

1. Flow temperature sensor fault – Check sensor connections and resistance; replace if cold resistance is not approximately 10kΩ at 25°C.
2. Diverter valve motor fault – Check the motor and wiring; replace the 3-way valve motor if necessary.
3. Hall Effect Sensor issue – Check for approx. 5V DC across red & blue wires; clean or replace if the rotor is not moving freely.
4. Obstructed heat exchanger – If the pump is running but heating is inconsistent, replace the heat exchanger.
5. Faulty temperature sensors – CH sensor should be ~10kΩ and flue sensor ~20kΩ at 25°C; replace if values are incorrect.

Each issue should be checked and addressed in sequence to restore consistent hot water heating.

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Summary of Contents for Baxi Duo-tec 2 Combi GA Range

Page 1 Installation & Servicing Instructions Duo-tec 2 Combi GA Range Gas Fired Wall Mounted Condensing Combination Boiler These instructions include the Benchmark Commissioning Checklist and should be left with the user for safe keeping. They must be read in conjunction with the Flue Installation Guide.
Page 2 UK and to encourage the regular servicing of all central heating systems to ensure safety and efficiency. © Baxi Heating UK Ltd 2013 All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, or stored in any...
Page 3: Installer Notification Guidelines
Benchmark Checklist ‘Gas Safe Register’ will issue a LABC will record the data Building Regulations Compliance and will issue a Certificate to the property owner certificate of compliance and inform the relevant LABC © Baxi Heating UK Ltd 2013...
Page 4 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. © Baxi Heating UK Ltd 2013...
Page 5 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 !! © Baxi Heating UK Ltd 2013...
Page 6: Table Of Contents
Site Requirements Flue Options Installation 10.0 Commissioning 11.0 Completion 12.0 Servicing 13.0 Changing Components 14.0 Combustion & Calibration 15.0 Electrical 16.0 Short Parts List 17.0 Fault Finding 18.0 External Low Voltage Controls Benchmark Checklist © Baxi Heating UK Ltd 2013...
Page 7: Introduction
1.0 Introduction Description 1. The Baxi Duo-tec 2 Combi GA Range are fully automatic gas fired wall mounted condensing combination boilers. It is room sealed and fan assisted, and will serve central heating and mains fed domestic hot water. 2. The boiler is set to give a maximum output of :- 24 models - 24 kW DHW 21.2 kW CH (Condensing)
Page 8: General Layout
Spark Ignition Electrode Combustion Box Cover & Burner Control Box Display Condensate Trap Safety Pressure Relief Valve Drain Off Point Gas Valve Diverter Valve Motor Boiler Controls Boiler Adaptor Heating Flow Sensor Safety Thermostat © Baxi Heating UK Ltd 2013...
Page 9: Appliance Operation
B – Heating Flow pump will automatically operate for 1 minute to prevent C – Domestic Hot Water Outlet sticking. D – Gas Inlet E – Cold Water Inlet On/Off Valve and filter F – Heating Return © Baxi Heating UK Ltd 2013...
Page 10: Technical Data
This value is used in the UK Government’s Standard and subject to normal production tolerances. Assessment Procedure (SAP) for energy rating of dwellings. The test data from which it has been calculated 1000 1200 Flow Rate (l/h) has been certified by 0087. © Baxi Heating UK Ltd 2013...
Page 11: Dimensions And Fixings
Valve (15mm) 50 mm 45 mm 65 mm 65 mm 65 mm 65 mm 95 mm 192 mm Heating Hot Water Cold Water Heating Flow Outlet Inlet Inlet Return (22mm) (15mm) (22mm) (15mm) (22mm) © Baxi Heating UK Ltd 2013...
Page 12: System Details
6.0 System Details Information 1. The Baxi Duo-tec Combi HE GA 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).
Page 13 5. A boiler discharge pump is available, part no. 720648301. This pump will dispose of both condensate & high temperature Pressure Relief Valve Discharge Pipe water from the relief valve. It has a maximum head of 5 metres. © Baxi Heating UK Ltd 2013...
Page 14 Fittings are intended to be used in the DHW therefore all pipework, connections, fittings, etc. should be system connected to a Baxi Duo-tec Combi GA suitable for pressures in excess of 8 bar. A pressure reducing it is strongly recommended that the DHW flow rate DOES NOT fall below 2.5l/min.
Page 15: Site Requirements
2. BS 5440: Part 2 refers to room sealed appliances installed in compartments. The appliance will run sufficiently cool without ventilation. 5mm Min 355mm (345mm with flap removed) In Operation Fig. 9 © Baxi Heating UK Ltd 2013...
Page 16 In IE reference should be made to the current edition of I.S. Outside Zones 813 “Domestic Gas Installations” and the current ETCI rules. 2.25 m Zone 1 Zone 2 Zone 0 0.6 m Fig. B In GB Only © Baxi Heating UK Ltd 2013...
Page 17 *It is NOT RECOMMENDED to connect upstream of the sink or other waste water receptacle ! © Baxi Heating UK Ltd 2013...
Page 18 45° iv) Termination to a purpose made soakaway Further specific requirements for soakaway Boiler design are referred to in BS 6798. 500mm min Holes in the soak-away must face away from the building © Baxi Heating UK Ltd 2013...
Page 19 Boiler External runs & those in unheated locations still require insulation. Condensate Pump Pipe must terminate above water level but below surrounding surface. Cut end at 45° © Baxi Heating UK Ltd 2013...
Page 20 Top View Rear Flue doors (see Fig. 13). Fig. 11 Property Boundary Line Air Inlet Opening Window or Door 150mm Fig. 13 MIN. Fig. 12 Likely flue positions requiring a flue terminal guard © Baxi Heating UK Ltd 2013...
Page 21: Flue Options
This bend is equivalent to 1 metre (ii) This bend is equivalent to 1 metre Total equivalent length = A+B+C+2 x 90° Bends © Baxi Heating UK Ltd 2013...
Page 22 Secure the deflector to the terminal with screws provided. Flue Accessories 1. For full details of Flue Accessories (elbows, extensions, clamps etc.) refer to the Flue Installation Guide supplied in the literature pack. © Baxi Heating UK Ltd 2013...
Page 23: Installation
Fig. 19 Flushing Flushing Tube 1. Connect a tube to the heating flow or return pipe (Fig. 20). 2. Flush thoroughly (see System Details, Section 6.2). Heating Flow Fig. 20 Heating Return © Baxi Heating UK Ltd 2007...
Page 24 3. The boiler condensate trap should be primed by pouring Rubber Hose approximately 300ml of water into the flue spigot (Fig. 22a). Fig. 23 Do not allow any water to fall into the air inlet. © Baxi Heating UK Ltd 2013...
Page 25 9. Using the clearance holes in the Connection Assembly secure it to the Terminal Assembly using the screws supplied (Fig. 28). Fig. 26 ‘TOP’ Label Securing Screw Sealing Tape Fig. 28 Fig. 27 ‘TOP’ Label © Baxi Heating UK Ltd 2013...
Page 26 17. Make good between the wall and air duct outside the building, appropriate to the wall construction and fire rating. 18. If necessary fit a terminal guard (see Section 8.4). Elbow to adaptor securing screws Slots at bottom Fig. 31 © Baxi Heating UK Ltd 2013...
Page 27 NOTE: The 230V switched signal for external controls (Frost Stat - Room Stat - Timer) must always be taken from terminal 2 at the boiler. Live, Neutral and Earth to power these controls must be taken from the Fused Spur. © Baxi Heating UK Ltd 2013...
Page 28: Commissioning
& • The integrity of the flue system and the flue seals. • The integrity of the boiler combustion circuit and the relevant seals. Proceed to put the boiler into operation as follows: © Baxi Heating UK Ltd 2013...
Page 29 . Press 4. Press to select the value that corresponds with the required gas type. For Natural Gas:- For Propane:- 5. Press to save the change, then to return to the normal display. © Baxi Heating UK Ltd 2013...
Page 30: Completion
& hot water. This will purge air from the system. The display will show 5. Once De-Aeration is complete set the external controls as required by the user. © Baxi Heating UK Ltd 2013...
Page 31: Servicing
4. Disconnect the condensate drain pipe and unscrew the sump Drain Pipe from the bottom of the condensate trap assembly (Fig. 44). Remove any deposits from the sump and trap. Clean as necessary and replace the sump. © Baxi Heating UK Ltd 2013...
Page 32 Benchmark Commissioning Checklist at the rear of this publication and then hand it back to the user. Hydraulic Inlet Assembly View underneath appliance Restrictor (not on 40 models) Fig. 48 Filter Fig. 47 DHW Isolation Cock © Baxi Heating UK Ltd 2013...
Page 33: Changing Components
5. When satisfactory combustion readings are not obtained ensure the electrode position is correct and perform the combustion check again. Control Box removed for clarity Spark Ignition Electrode Electrode Leads Flame Sensing Electrode Fig. 49 © Baxi Heating UK Ltd 2013...
Page 34 5. Examine the gasket and replace if necessary. 6. After changing the venturi check the combustion - see Fig. 50 Section 14.1. Gas Feed Pipe Venturi Gasket Fig. 51 © Baxi Heating UK Ltd 2013...
Page 35 Keep the insulation vertical and press firmly into position. 8. Examine the cover seal and replace if necessary. Reassemble in reverse order. Air/Gas Collector Spark Ignition Electrode Cover Insulation Seal Fig. 53 Electrode Flame Sensing Leads Electrode © Baxi Heating UK Ltd 2013...
Page 36 3. Prise off the spring clip and remove the sensor. Examine DHW NTC Sensor the ‘O’ ring, replacing if necessary. Pump, Gas Valve Assemblies and Pipework 4. Reassemble in reverse order. removed for clarity Fig. 56 © Baxi Heating UK Ltd 2013...
Page 37 2. The automatic air vent is a bayonet fitting. Remove by twisting anticlockwise. 3. Fit the new automatic air vent, ensuring the ‘O’ ring is fitted and the cap is open . Reassemble in reverse order. Fig. 58 © Baxi Heating UK Ltd 2013...
Page 38 Fig. 59 integrity of the case seal. ‘O’ ring seal Fig. 61a Grub Screw Pressure Gauge Safety Pressure Capillary Relief Valve Fig. 60 Discharge Pipe © Baxi Heating UK Ltd 2013...
Page 39 6. Remove the valve assembly. Examine all seals and washers, replacing if necessary. Transfer the DHW NTC and hydraulic pressure sensor to the new valve and reassemble in reverse order. © Baxi Heating UK Ltd 2013...
Page 40 7. P.C.B. & R.D.S. changed - enable the Calibration Function as described in Section 14.2, then Check the Combustion - see Section 14.1. Note the correct orientation of the R.D.S. Position with the chamfer as shown. © Baxi Heating UK Ltd 2013...
Page 41 4. Whilst supporting the vessel undo and remove the locknut securing the vessel spigot to the boiler top panel. 5. Manoeuvre the vessel out of the boiler. 6. Reassemble in reverse order. Support Bracket Fig. 66 © Baxi Heating UK Ltd 2013...
Page 42: Combustion & Calibration
Minimum fan speeds. Press & together and hold intervals. for at least 6 seconds to exit the function. ‘ESC’ 5. To exit the function press will be displayed and the calibration function completed. © Baxi Heating UK Ltd 2013...
Page 43: Electrical
Diverter Valve Motor Key To Wiring Colours b - Blue r - Red bk - Black g - Green br - Brown g/y - Green/Yellow w - White y - Yellow gr - Grey © Baxi Heating UK Ltd 2013...
Page 44: Short Parts List
Injector Washer - 28 (Ø 4.6) 720775801 Injector Washer - 33 (Ø 4.9) 720776001 Injector Washer - 40 (Ø 5.8) 720786601 Air/Gas Venturi (24 & 28) 720768301 Air/Gas Venturi 33 720785401 Air/Gas Venturi 40 720785601 © Baxi Heating UK Ltd 2013...
Page 45: Error Codes
‘25’ 8. Press until is displayed. Confirm with then press to return the display to normal. 4. If this does not have any effect, or the codes are displayed regularly further investigation is required. © Baxi Heating UK Ltd 2013...
Page 46: Fault Finding Operational Sequence
Go to section ‘K’ Heating circuit Burner modulates to maintain Check Heating flow sensor. set temperature Go to section ‘D’ Go to section ‘M’ 130 flashing Fan stops after 10 seconds Boiler operation correct Burner goes out © Baxi Heating UK Ltd 2013...
Page 47 Domestic Hot Water circuit Check CH NTC sensor. Burner modulates to maintain set temperature Go to section ‘D’ Go to section ‘M’ 130 flashing Fan stops after 10 seconds Boiler operation correct Burner goes out © Baxi Heating UK Ltd 2013...
Page 48: Fault Finding Solutions Sections
10kë @ 25° C (DHW and CH sensors) Replace sensor (resistance reduces with increase in temp.) Gas at burner Ensure gas is on and purged Check wiring and PCB - X36 connector Replace gas valve see Wiring Diagram Replace PCB © Baxi Heating UK Ltd 2013...
Page 49 Check for and correct any faulty system faults Allow to cool. Continuity across thermostat terminals Replace safety thermostat more than 1.5 ohm Check Flow & Return Sensors - 110 still flashing ? see section ‘D’ Replace PCB © Baxi Heating UK Ltd 2013...
Page 50 Cold resistance approximately 10kë @ 25° C (CH sensor) Replace sensor 20kë @ 25° C (Flue sensor) (resistance reduces with increase in temp.) If pump is running the heat exchanger could be Replace heat exchanger obstructed © Baxi Heating UK Ltd 2013...
Page 51: External Low Voltage Controls
18.0 External Low Voltage Controls Optional Outdoor Sensor 1/2 H 2.5m Min West North Boiler Flow Temperature Outdoor Temperature © Baxi Heating UK Ltd 2013...
Page 52 Terminal M2 Voltage 1 2 3 Terminal Block Boiler IMPORTANT ! IMPORTANT ! Mains When fitting Low Voltage Voltage Controls Terminal remove the Yellow Link Wire Block M1 from the Boiler Terminal Block M1 © Baxi Heating UK Ltd 2013...
Page 53 Boiler Wiring Terminal M2 Voltage Terminal Block Boiler Mains IMPORTANT ! IMPORTANT ! Voltage When fitting Low Voltage Terminal Controls remove the Block M1 Yellow Link Wire from the Boiler Terminal Block M1 © Baxi Heating UK Ltd 2013...
Page 54: Benchmark Checklist
GAS BOILER SYSTEM COMMISSIONING CHECKLIST This Commissioning Checklist is to be completed in full by the competent person who commissioned the boiler as a means of demonstrating compliance with the appropriate Building Regulations and then handed to the customer to keep for future reference. Failure to install and commission according to the manufacturer’s instructions and complete this Benchmark Commissioning Checklist will invalidate the warranty.
Page 55: Service Record
Service Record It is recommended that your heating system is serviced regularly and that the appropriate Service Interval Record is completed. Service Provider Before completing the appropriate Service Record below, please ensure you have carried out the service as described in the manufacturer’s instructions.
Page 56 A Tr a d i n g D i v i si o n of Bax i H eati ng UK Lt d (3879156) Brooks House, Coventry Road, Warwick. CV34 4LL After Sales Service 0844 871 1525 Technical Enquiries 0844 871 1555 Website www.baxi.co.uk e&oe Comp No. 7206334 - 08 (5/13) © Baxi Heating UK Ltd 2013...

This manual is also suitable for:

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