Baxi
The Baxi 824 Combi 2 is a 24 kW natural gas and LPG compatible combi boiler, offering a 14.1 lpm DHW flow rate and an ErP A-rating for both heating and hot water.
The Baxi 824 Combi 2 is a wall-hung condensing combi boiler designed for domestic heating and hot water in UK properties. This appliance operates on natural gas or LPG and provides a maximum central heating output of 20 kW and a domestic hot water output of 24 kW. It is engineered for straightforward installation and maintenance, offering a reliable solution for heating engineers. This page details its technical specifications, performance data, and common fault codes to assist with servicing and diagnostics.
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Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
Diagrammed on page 17
All recirculatory water systems will be subject to corrosion unless an appropriate water treatment is applied. A suitable inhibitor must then be added to the system.
The Baxi 824 Combi 2 delivers a seasonal efficiency of 99% and holds an ErP A-rating for both heating and domestic hot water, with an XL DHW profile. Its compact dimensions, measuring 700mm high, 395mm wide, and 285mm deep, allow for flexible installation within various property layouts. The boiler provides a domestic hot water flow rate of 14.1 litres per minute at a 30°C temperature rise, suitable for typical household demands. For central heating, it offers a modulated output range from 4.8 kW to 20 kW. The unit is designed for wall-hung installation and features a dry weight of 28 kg. It incorporates safety features such as overheat protection and frost protection, ensuring operational reliability. Compatibility with OpenTherm room units and weather compensation controls further enhances its adaptability within modern heating systems. NOx emissions are rated at Class 6, with 32 mg/kWh.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/boilers/baxi/830-combi-2#fault-a.00.34 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| A.00.34 | Outdoor temperature sensor expected but not detected Show causes & actionsLikely causes
Engineer action Connect the outdoor sensor | Details |
| A.02.06 | Low water pressure Show causes & actionsLikely causes
Engineer action Check the system pressure and restore it Check the pressure of the expansion vessel | Details |
| A.02.18 | OBD error Show causes & actionsEngineer action Re-enter the CN1 and CN2 values, check the information shown on the data plate | Details |
| A.02.36 | Functional device disconnected Show causes & actionsLikely causes
Engineer action SCB BOARD NOT DETECTED Faulty SCB, replace the board | Details |
| A.02.37 | Passive functional device disconnected Show causes & actionsLikely causes
Engineer action SCB BOARD NOT DETECTED Faulty SCB, replace the board | Details |
| A.02.45 | Connection error Show causes & actionsEngineer action SCB BOARD NOT DETECTED Carry out the auto-detect function | Details |
| A.02.46 | Device priority error Show causes & actionsEngineer action SCB BOARD NOT DETECTED Carry out the auto-detect function | Details |
| A.02.48 | Unit function configuration error Show causes & actionsEngineer action SCB BOARD NOT DETECTED Carry out the auto-detect function | Details |
| A.02.49 | Failed node initialisation Show causes & actionsEngineer action SCB BOARD NOT DETECTED Carry out the auto-detect function | Details |
| A.02.54 | Open Therm bus power supply error Show causes & actionsEngineer action Replace the CU-GH board | Details |
| A.02.55 | Incorrect or missing serial number Show causes & actionsEngineer action Replace the CU-GH board | Details |
| A.02.76 | Internal memory reserved for full customisation of settings. No further changes can be made Show causes & actionsEngineer action CONFIGURATION ERROR Re-enter the values CN1 and CN2 Replace the CU-GH board | Details |
| H.00.42 | Pressure sensor open/faulty Show causes & actionsEngineer action No action required | Details |
| H.01.00 | Temporary communication failure between gas valve and boiler PCB. Show causes & actionsEngineer action MAIN PCB ERROR Configure CN1/CN2 Replace the main PCB | Details |
| H.01.05 | Maximum temperature difference value between flow and return reached. Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION Check the boiler/installation circulation Activate a manual venting cycle Check the installation pressure | Details |
| H.01.08 | Flow temperature increase in heating mode too quick. Temporary stoppage of 10 minutes. Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION Check the boiler/installation circulation Activate a manual venting cycle Check the installation pressure | Details |
| H.01.14 | Maximum flow temperature value reached. Show causes & actionsEngineer action INSUFFICIENT CIRCULATION Check the boiler/installation circulation Activate a manual venting cycle | Details |
| H.01.18 | No water circulation (temporary). Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION Check the installation pressure Activate a manual venting cycle Check the operation of the pump Check the boiler/installation circulation TEMPERATURE SENSOR ERROR | Details |
| H.01.21 | Flow temperature increase in domestic water mode too quick. Temporary stoppage of 10 minutes. Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION Check the installation pressure Activate a manual venting cycle Check the operation of the pump Check the boiler/installation circulation TEMPERATURE SENSOR ERROR | Details |
| H.02.00 | Reset in progress Show causes & actionsEngineer action CN1/CN2 CONFIGURATION MISSING Configure CN1/CN2 | Details |
| H.02.02 | Waiting for configuration settings to be entered (CN1,CN2). Show causes & actionsEngineer action Check configuration CN1/CN2 Configure CN1/CN2 correctly | Details |
| H.02.03 | Configuration settings (CN1, CN2) not entered correctly. Show causes & actionsEngineer action MAIN PCB ERROR Configure CN1/CN2 | Details |
| H.02.04 | PCB settings cannot be read. Show causes & actionsEngineer action Replace the main PCB | Details |
| H.02.05 | Setting memory not compatible with the boiler PCB type Show causes & actionsEngineer action Replace the main PCB | Details |
| H.02.07 | Low pressure in heating circuit (permanently) Show causes & actionsLikely causes
Engineer action Check the system pressure and restore it Check the pressure of the expansion vessel | Details |
| H.02.09 | Partial stoppage of the boiler Show causes & actionsLikely causes
Engineer action SIGNAL INDICATING BLOCKING INPUT ACTIVE OR FROST PROTECTION ACTIVE | Details |
| H.02.10 | Complete stoppage of the boiler Show causes & actionsLikely causes
Engineer action BLOCKING INPUT SIGNAL (WITHOUT FROST PROTECTION) | Details |
| H.02.12 | Opening of the control unit input signal contact from the external device Show causes & actionsEngineer action Not possible | Details |
| H.02.38 | No water hardness Show causes & actionsEngineer action SCB-09 board error | Details |
| H.02.70 | External unit heat recovery test failed Show causes & actionsEngineer action MAIN PCB ERROR Replace the main PCB | Details |
| H.03.00 | No identification data for boiler safety device. Show causes & actionsEngineer action MAIN PCB ERROR Replace the main PCB | Details |
| H.03.01 | Communication failure in comfort circuit (internal fault in boiler PCB). Show causes & actionsEngineer action MAIN PCB ERROR Replace the main PCB | Details |
| H.03.02 | Temporary flame loss Show causes & actionsLikely causes
Engineer action ELECTRODE PROBLEM GAS SUPPLY FLUE GAS PIPES | Details |
| H.03.05 | Power supply voltage too low Show causes & actionsEngineer action Check the mains voltage | Details |
| H.03.17 | Periodic safety check in progress Show causes & actionsEngineer action ELECTRODE PROBLEM Check the electrode electrical connections Check the condition of the electrode GAS SUPPLY | Details |
| H.03.54 | Temporary flame loss Shutdown due to the power supply voltage being too low Show causes & actionsLikely causes
Engineer action ELECTRODE PROBLEM GAS SUPPLY FLUE GAS EXHAUST PIPE | Details |
| E.00.04Lockout | Return temperature sensor disconnected Show causes & actionsLikely causes
Engineer action SENSOR/CONNECTION PROBLEM | Details |
| E.00.05Lockout | Return temperature sensor short circuited Show causes & actionsLikely causes
Engineer action SENSOR/CONNECTION PROBLEM | Details |
| E.00.06Lockout | Return sensor expected but not detected Show causes & actionsEngineer action SENSOR/CONNECTION PROBLEM | Details |
| E.00.07Lockout | The difference in return temperature is too great Show causes & actionsEngineer action SENSOR OPEN | Details |
| E.00.16Lockout | DHW tank temperature sensor not connected Show causes & actionsLikely causes
Engineer action SENSOR OPEN | Details |
| E.00.17Lockout | DHW tank temperature sensor short-circuited Show causes & actionsLikely causes
Engineer action SENSOR CLOSED | Details |
| E.00.20Lockout | The flue gas temperature sensor has short-circuited or measured a temperature below the range | — |
| E.00.21Lockout | The flue gas temperature sensor has short-circuited or measured a temperature above the range | — |
| E.01.04Lockout | Flame loss detected five times in 24 hours (with burner on) Show causes & actionsLikely causes
Engineer action GAS SUPPLY | Details |
| E.01.12Lockout | Temperature measured by return sensor greater than flow temperature Show causes & actionsLikely causes
Engineer action SENSOR/CONNECTION PROBLEM | Details |
| E.01.17Lockout | No water circulation (permanent) Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION SENSOR ERROR | Details |
| E.01.20Lockout | Maximum flue gas temperature reached Show causes & actionsLikely causes
Engineer action EXCHANGER ON FLUE GAS SIDE BLOCKED | Details |
| E.02.13Lockout | Stoppage input for the device external environment control unit | — |
| E.02.15Lockout | External PCB communication timeout Show causes & actionsEngineer action MAIN PCB ERROR Check for any electromagnetic interference Replace the main PCB | Details |
| E.02.17Lockout | Permanent communication failure between gas valve and boiler PCB Show causes & actionsEngineer action MAIN PCB ERROR Check for any electromagnetic interference Replace the main PCB | Details |
| E.02.35Lockout | Critical safety device disconnected Show causes & actionsEngineer action COMMUNICATION FAULT Carry out the auto-detect function | Details |
| E.02.47Lockout | Connection to external device unsuccessful Show causes & actionsEngineer action ELECTRICAL CONNECTION ERROR Possible cancellation, carry out the auto-detect function or re-enter the CN code | Details |
| E.04.00Lockout | Level 5 safety settings incorrect Show causes & actionsEngineer action BOILER PCB FAULT Replace the PCB | Details |
| E.04.01Lockout | Flow temperature sensor short circuited Show causes & actionsLikely causes
Engineer action SENSOR/CONNECTION PROBLEM | Details |
| E.04.02Lockout | Flow temperature sensor disconnected Show causes & actionsLikely causes
Engineer action SENSOR/CONNECTION PROBLEM | Details |
| E.04.03Lockout | Maximum flow temperature exceeded Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION | Details |
| E.04.07Lockout | Difference between the temperature values detected by flow sensors 1 and 2 | — |
| E.04.08Lockout | Maximum safe temperature value reached Show causes & actionsLikely causes
Engineer action INSUFFICIENT CIRCULATION OTHER POSSIBLE CAUSES | Details |
| E.04.09Lockout | Difference between the temperature values detected by flue gas sensors 1 and 2 | — |
| E.04.10Lockout | Burner failed to ignite after 4 attempts Show causes & actionsLikely causes
Engineer action GAS SUPPLY ELECTRODE PROBLEM OTHER CAUSES | Details |
| E.04.11Lockout | VPS gas valve test failed Show causes & actionsEngineer action Check the ground circuit Check the power supply voltage | Details |
| E.04.12Lockout | Ignition failure for monitoring parasitic flame Show causes & actionsEngineer action Check the ground circuit Check the power supply voltage | Details |
| E.04.13Lockout | Fan blade blocked Show causes & actionsEngineer action FAN/PCB PROBLEM Check the PCB-fan connection Replace the air-gas unit | Details |
| E.04.14Lockout | The temperature difference between the set point and the burner varies more than 60 s compared to the GVC configuration | — |
| E.04.15Lockout | Flue gas exhaust pipe blocked Show causes & actionsEngineer action MAIN PCB ERROR Replace the main PCB | Details |
| E.04.17Lockout | Fault in gas valve control circuit Show causes & actionsEngineer action MAIN PCB ERROR Replace the main PCB | Details |
| E.04.18Lockout | The flow temperature measured is lower than the minimum temperature defined by the GVC setting | — |
| E.04.19Lockout | Mass flow rate sensor communication error | — |
| E.04.20Lockout | Mass flow rate sensor maximum deviation | — |
| E.04.21Lockout | Difference detected between the burner 1 and 2 temperature sensors Show causes & actionsEngineer action Not possible | Details |
| E.04.23Lockout | Gas valve check valve internal stoppage | — |
| E.04.24Lockout | Gas family not detected during the automatic detection function Show causes & actionsEngineer action Not possible | Details |
| E.04.54Lockout | Fault in gas valve control circuit Show causes & actionsEngineer action Check the wiring on the gas valve Replace the gas valve or PCB | Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Engineer: SENSOR/CONNECTION PROBLEM
Triggered by fault code E.00.04.
Engineer: SENSOR/CONNECTION PROBLEM
Triggered by fault code E.00.05.
Engineer: SENSOR/CONNECTION PROBLEM
Triggered by fault code E.00.06.
Engineer: SENSOR OPEN
Triggered by fault code E.00.07.
Engineer: SENSOR OPEN
Triggered by fault code E.00.16.
Diagnostic checklists from engineer-submitted Baxi faults, with step-by-step checks and safety notes.
The Baxi 800 boiler intermittently heating without a fault code can be attributed to several common issues, including low system pressure,…
The Baxi 100HE displaying an 'Ignition Lockout' fault, with no heating or hot water and no noises, indicates the boiler has failed to…
The Baxi 824 Combi 2 displaying fault code E.04.10 indicates that the burner has failed to ignite after four attempts.
Common questions from engineers and homeowners about the Baxi 830 Combi 2.
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Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 28 June 2026.