Product error-code directory

Boilers and HVAC error codes

Search fault, warning and status codes for boilers, air conditioners, heat pumps, thermostats and ventilation equipment. Find quick meanings, model context, safe checks and available source guidance.

2,693documented codes
32manufacturers
30product groups

About Boilers and HVAC error codes

Error codes are diagnostic indicators generated when a product detects an operating condition outside its expected range. They help narrow the search, but they do not automatically prove that a named component has failed. The same code can have different meanings across manufacturers, products, model generations and regions.

This category directory covers boilers, air conditioners, heat pumps, thermostats and ventilation equipment. Start with the exact characters shown on the display, then confirm the manufacturer, product type and full model number. Every indexed result links to a dedicated page containing a quick answer, likely symptoms and causes, safe troubleshooting boundaries, reset guidance, applicable products and source information.

Do not repeatedly reset a returning fault or use instructions written for a different model. Isolate electrical products before accessible checks and stop where gas, refrigerant, high voltage, stored energy, hot components or moving machinery may be involved. Use an authorised technician whenever diagnosis requires covers to be removed or safety-critical systems to be tested.

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103ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 103 error code – Flow check failed three times; last failure check 1ATAG identifies code 103 as: Flow check failed three times; last failure check 1.104ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 104 error code – Flow check failedATAG identifies code 104 as: Flow check failed.105ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 105 error code – Flow check failed three times; last failure check 3ATAG identifies code 105 as: Flow check failed three times; last failure check 3.106ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 106 error code – Flow check failed three times; last failure check 4ATAG identifies code 106 as: Flow check failed three times; last failure check 4.107ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 107 error code – Flow check 5 failedATAG identifies code 107 as: Flow check 5 failed.108ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 108 error code – Water pressure below 0.5 bar; filling neededATAG identifies code 108 as: Water pressure below 0.5 bar; filling needed.109ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 109 error code – Water pressure above maximumATAG identifies code 109 as: Water pressure above maximum.110ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 110 error code – Flow temperature probe damagedATAG identifies code 110 as: Flow temperature probe damaged.112ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 112 error code – Return temperature probe damagedATAG identifies code 112 as: Return temperature probe damaged.114ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 114 error code – Outdoor temperature sensor damagedATAG identifies code 114 as: Outdoor temperature sensor damaged.118ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 118 error code – Flow and return probe plausibility check failedATAG identifies code 118 as: Flow and return probe plausibility check failed.140ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 140 error code – Dynamic pressure check failed or pump not detectedATAG identifies code 140 as: Dynamic pressure check failed or pump not detected.141ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 141 error code – Central-heating flow switch openATAG identifies code 141 as: Central-heating flow switch open.1P1ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 1P1 error code – Flow check 1 failedATAG identifies code 1P1 as: Flow check 1 failed.1P2ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 1P2 error code – Flow check 3 failedATAG identifies code 1P2 as: Flow check 3 failed.1P3ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 1P3 error code – Flow check 4 failedATAG identifies code 1P3 as: Flow check 4 failed.1P4ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 1P4 error code – Water pressure between 0.5 and 0.8 bar; filling neededATAG identifies code 1P4 as: Water pressure between 0.5 and 0.8 bar; filling needed.1P9ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 1P9 error code – Dynamic water-pressure checkATAG identifies code 1P9 as: Dynamic water-pressure check.201ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 201 error code – Domestic hot-water probe damagedATAG identifies code 201 as: Domestic hot-water probe damaged.203ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 203 error code – Cylinder probe damagedATAG identifies code 203 as: Cylinder probe damaged.303ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 303 error code – PCB faultATAG identifies code 303 as: PCB fault.304ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 304 error code – Too many resetsATAG identifies code 304 as: Too many resets.306ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 306 error code – PCB faultATAG identifies code 306 as: PCB fault.309ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 309 error code – Gas relay check failedATAG identifies code 309 as: Gas relay check failed.41ZATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 41Z error code – Room sensor zone unavailableATAG identifies code 41Z as: Room sensor zone unavailable.501ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 501 error code – No flame detectedATAG identifies code 501 as: No flame detected.502ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 502 error code – Flame detected with gas valve closedATAG identifies code 502 as: Flame detected with gas valve closed.504ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 504 error code – Flame lift detectedATAG identifies code 504 as: Flame lift detected.5P2ATAG · ATAG iC, iS and iR boiler range — 2019 and newer · United KingdomATAG 5P2 error code – First ignition attempt failedATAG identifies code 5P2 as: First ignition attempt failed.A.00.28Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomSolar temperature sensor is either removed or measures a temperature below range.Baxi documents A.00.28 for the Baxi 600/800 Combi and System 2 boilers as “Solar temperature sensor is either…A.00.29Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomSolar temperature sensor is either shorted or measures a temperature above range.Baxi documents A.00.29 for the Baxi 600/800 Combi and System 2 boilers as “Solar temperature sensor is either…A.00.34Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomOutdoor temperature sensor expected but not detected.Baxi documents A.00.34 for the Baxi 600/800 Combi and System 2 boilers as “Outdoor temperature sensor expected but…A.02.06Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomLow system pressure in heating circuit.Baxi documents A.02.06 for the Baxi 600/800 Combi and System 2 boilers as “Low system pressure in heating…A.02.18Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomOBD error.Baxi documents A.02.18 for the Baxi 600/800 Combi and System 2 boilers as “OBD error.”. This is the…A.02.36Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFunctional device disconnected.Baxi documents A.02.36 for the Baxi 600/800 Combi and System 2 boilers as “Functional device disconnected.”. This is…A.02.37Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomPassive functional device disconnected.Baxi documents A.02.37 for the Baxi 600/800 Combi and System 2 boilers as “Passive functional device disconnected.”. This…A.02.45Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomConnection error.Baxi documents A.02.45 for the Baxi 600/800 Combi and System 2 boilers as “Connection error.”. This is the…A.02.46Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomDevice priority error.Baxi documents A.02.46 for the Baxi 600/800 Combi and System 2 boilers as “Device priority error.”. This is…A.02.48Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomUnit function configuration error.Baxi documents A.02.48 for the Baxi 600/800 Combi and System 2 boilers as “Unit function configuration error.”. This…A.02.49Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFailed node initialisation.Baxi documents A.02.49 for the Baxi 600/800 Combi and System 2 boilers as “Failed node initialisation.”. This is…A.02.54Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomOpenTherm bus power supply error.Baxi documents A.02.54 for the Baxi 600/800 Combi and System 2 boilers as “OpenTherm bus power supply error.”.…A.02.55Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomIncorrect or missing serial number.Baxi documents A.02.55 for the Baxi 600/800 Combi and System 2 boilers as “Incorrect or missing serial number.”.…A.02.76Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomInternal memory reserved for full customisation of settings. No further changes can be made.Baxi documents A.02.76 for the Baxi 600/800 Combi and System 2 boilers as “Internal memory reserved for full…E.00.04Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomReturn temperature sensor disconnected.Baxi documents E.00.04 for the Baxi 600/800 Combi and System 2 boilers as “Return temperature sensor disconnected.”. This…E.00.05Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomReturn temperature sensor short circuited.Baxi documents E.00.05 for the Baxi 600/800 Combi and System 2 boilers as “Return temperature sensor short circuited.”.…E.00.16Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomDHW tank temperature sensor not connected.Baxi documents E.00.16 for the Baxi 600/800 Combi and System 2 boilers as “DHW tank temperature sensor not…E.00.17Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomDHW tank temperature sensor short-circuited.Baxi documents E.00.17 for the Baxi 600/800 Combi and System 2 boilers as “DHW tank temperature sensor short-circuited.”.…E.00.20Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomThe flue gas temperature sensor is not connected or measured a temperature below the range.Baxi documents E.00.20 for the Baxi 600/800 Combi and System 2 boilers as “The flue gas temperature sensor…E.00.21Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomThe flue gas temperature sensor has short-circuited or measured a temperature above the range.Baxi documents E.00.21 for the Baxi 600/800 Combi and System 2 boilers as “The flue gas temperature sensor…E.01.04Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFlame loss detected five times in 24 hours.Baxi documents E.01.04 for the Baxi 600/800 Combi and System 2 boilers as “Flame loss detected five times…E.01.12Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomTemperature measured by return sensor greater than flow temperature.Baxi documents E.01.12 for the Baxi 600/800 Combi and System 2 boilers as “Temperature measured by return sensor…E.01.17Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomNo water circulation (permanent).Baxi documents E.01.17 for the Baxi 600/800 Combi and System 2 boilers as “No water circulation (permanent).”. This…E.01.20Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomMaximum flue gas temperature reached.Baxi documents E.01.20 for the Baxi 600/800 Combi and System 2 boilers as “Maximum flue gas temperature reached.”.…E.02.13Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomTotal stoppage of the boiler (antifreeze function not active).Baxi documents E.02.13 for the Baxi 600/800 Combi and System 2 boilers as “Total stoppage of the boiler…E.02.17Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomPermanent communication failure between gas valve and boiler PCB.Baxi documents E.02.17 for the Baxi 600/800 Combi and System 2 boilers as “Permanent communication failure between gas…E.02.35Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomCritical safety device disconnected.Baxi documents E.02.35 for the Baxi 600/800 Combi and System 2 boilers as “Critical safety device disconnected.”. This…E.02.39Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomMinimum pressure not reached after 6 minutes of automatic filling.Baxi documents E.02.39 for the Baxi 600/800 Combi and System 2 boilers as “Minimum pressure not reached after…E.02.47Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomConnection to external device unsuccessful.Baxi documents E.02.47 for the Baxi 600/800 Combi and System 2 boilers as “Connection to external device unsuccessful.”.…E.04.01Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFlow temperature sensor short circuited.Baxi documents E.04.01 for the Baxi 600/800 Combi and System 2 boilers as “Flow temperature sensor short circuited.”.…E.04.02Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFlow temperature sensor disconnected.Baxi documents E.04.02 for the Baxi 600/800 Combi and System 2 boilers as “Flow temperature sensor disconnected.”. This…E.04.03Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomMaximum flow temperature exceeded or flow temperature sensor short circuited.Baxi documents E.04.03 for the Baxi 600/800 Combi and System 2 boilers as “Maximum flow temperature exceeded or…E.04.08Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomMaximum safe temperature value reached.Baxi documents E.04.08 for the Baxi 600/800 Combi and System 2 boilers as “Maximum safe temperature value reached.”.…E.04.10Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomBurner failed to ignite after 4 attempts.Baxi documents E.04.10 for the Baxi 600/800 Combi and System 2 boilers as “Burner failed to ignite after…E.04.12Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomIgnition failure -flame monitoring.Baxi documents E.04.12 for the Baxi 600/800 Combi and System 2 boilers as “Ignition failure -flame monitoring.”. This…E.04.13Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFan impeller blocked or maximum rpm exceeded.Baxi documents E.04.13 for the Baxi 600/800 Combi and System 2 boilers as “Fan impeller blocked or maximum…E.04.17Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFault in gas valve control circuit.Baxi documents E.04.17 for the Baxi 600/800 Combi and System 2 boilers as “Fault in gas valve control…E.04.18Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomThe flow temperature is below the minimum temperature or the flow temperature sensor is not connected.Baxi documents E.04.18 for the Baxi 600/800 Combi and System 2 boilers as “The flow temperature is below…E.04.23Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomCommunication internal stoppage.Baxi documents E.04.23 for the Baxi 600/800 Combi and System 2 boilers as “Communication internal stoppage.”. This is…E.04.254Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFault in gas valve control circuit.Baxi documents E.04.254 for the Baxi 600/800 Combi and System 2 boilers as “Fault in gas valve control…E.04.29Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomCommunication internal stoppage.Baxi documents E.04.29 for the Baxi 600/800 Combi and System 2 boilers as “Communication internal stoppage.”. This is…E.04.54Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFault in gas valve control circuit.Baxi documents E.04.54 for the Baxi 600/800 Combi and System 2 boilers as “Fault in gas valve control…H.00.42Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomPressure sensor open/faulty.Baxi documents H.00.42 for the Baxi 600/800 Combi and System 2 boilers as “Pressure sensor open/faulty.”. This is…H.00.81Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomRoom unit disconnected.Baxi documents H.00.81 for the Baxi 600/800 Combi and System 2 boilers as “Room unit disconnected.”. This is…H.01.00Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomTemporary communication failure between gas valve and boiler PCB.Baxi documents H.01.00 for the Baxi 600/800 Combi and System 2 boilers as “Temporary communication failure between gas…H.01.05Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomMaximum temperature difference value between flow and return reached.Baxi documents H.01.05 for the Baxi 600/800 Combi and System 2 boilers as “Maximum temperature difference value between…H.01.08Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFlow temperature increase in heating mode too quick. Temporary stoppage of 10 minutes.Baxi documents H.01.08 for the Baxi 600/800 Combi and System 2 boilers as “Flow temperature increase in heating…H.01.14Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomMaximum flow or return temperature value reached.Baxi documents H.01.14 for the Baxi 600/800 Combi and System 2 boilers as “Maximum flow or return temperature…H.01.18Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomNo water circulation (temporary).Baxi documents H.01.18 for the Baxi 600/800 Combi and System 2 boilers as “No water circulation (temporary).”. This…H.01.21Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomFlow temperature increase during domestic hot water operation too fast.Baxi documents H.01.21 for the Baxi 600/800 Combi and System 2 boilers as “Flow temperature increase during domestic…H.02.00Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomReset in progress.Baxi documents H.02.00 for the Baxi 600/800 Combi and System 2 boilers as “Reset in progress.”. This is…H.02.02Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomWaiting for configuration settings to be entered (CN1,CN2).Baxi documents H.02.02 for the Baxi 600/800 Combi and System 2 boilers as “Waiting for configuration settings to…H.02.03Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomConfiguration settings (CN1,CN2) not entered correctly.Baxi documents H.02.03 for the Baxi 600/800 Combi and System 2 boilers as “Configuration settings (CN1,CN2) not entered…H.02.04Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomPCB settings cannot be read.Baxi documents H.02.04 for the Baxi 600/800 Combi and System 2 boilers as “PCB settings cannot be read.”.…H.02.05Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomSetting memory not compatible with the boiler PCB type.Baxi documents H.02.05 for the Baxi 600/800 Combi and System 2 boilers as “Setting memory not compatible with…H.02.07Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomLow pressure in heating circuit (permanently).Baxi documents H.02.07 for the Baxi 600/800 Combi and System 2 boilers as “Low pressure in heating circuit…H.02.09Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomPartial stoppage of the boiler (antifreeze function active).Baxi documents H.02.09 for the Baxi 600/800 Combi and System 2 boilers as “Partial stoppage of the boiler…H.02.10Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomTotal stoppage of the boiler (antifreeze function not active).Baxi documents H.02.10 for the Baxi 600/800 Combi and System 2 boilers as “Total stoppage of the boiler…H.02.70Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomExternal unit heat recovery test failed.Baxi documents H.02.70 for the Baxi 600/800 Combi and System 2 boilers as “External unit heat recovery test…H.03.00Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomNo identification data for boiler safety device.Baxi documents H.03.00 for the Baxi 600/800 Combi and System 2 boilers as “No identification data for boiler…H.03.02Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomTemporary flame loss.Baxi documents H.03.02 for the Baxi 600/800 Combi and System 2 boilers as “Temporary flame loss.”. This is…H.03.05Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomPower supply voltage too low.Baxi documents H.03.05 for the Baxi 600/800 Combi and System 2 boilers as “Power supply voltage too low.”.…H.03.54Baxi · Baxi 600/800 Combi and System 2 boilers · United KingdomTemporary flame loss. Shutdown due to the power supply voltage being too low.Baxi documents H.03.54 for the Baxi 600/800 Combi and System 2 boilers as “Temporary flame loss. Shutdown due…E09Baxi · Baxi legacy combi and system boilers · United KingdomGas valve connection fault.Baxi documents E09 for the Baxi legacy combi and system boilers as “Gas valve connection fault.”. This is…E10Baxi · Baxi legacy combi and system boilers · United KingdomExternal probe fault.Baxi documents E10 for the Baxi legacy combi and system boilers as “External probe fault.”. This is the…E103Baxi · Baxi legacy combi and system boilers · United KingdomSafety Assist battery is exhausted.Baxi documents E103 for the Baxi legacy combi and system boilers as “Safety Assist battery is exhausted.”. This…E104Baxi · Baxi legacy combi and system boilers · United KingdomFaulty Safety Assist PCB.Baxi documents E104 for the Baxi legacy combi and system boilers as “Faulty Safety Assist PCB.”. This is…E107Baxi · Baxi legacy combi and system boilers · United KingdomPCBs not synchronised.Baxi documents E107 for the Baxi legacy combi and system boilers as “PCBs not synchronised.”. This is the…E109Baxi · Baxi legacy combi and system boilers · United KingdomPrecirculation alarm.Baxi documents E109 for the Baxi legacy combi and system boilers as “Precirculation alarm.”. This is the quick…E110Baxi · Baxi legacy combi and system boilers · United Kingdom(i) Boiler max. temperature exceeded for gradient (probable pump jammed or air in the circuit). (ii) Safety thermostat sensor tripped.Baxi documents E110 for the Baxi legacy combi and system boilers as “(i) Boiler max. temperature exceeded for…E118Baxi · Baxi legacy combi and system boilers · United KingdomWater pressure LOW (<0.5 bar).Baxi documents E118 for the Baxi legacy combi and system boilers as “Water pressure LOW (<0.5 bar).”. This…