BoilerFaultCodes 254
Fault shown when using a non-Baxi Room Unit
Baxi 424 COMBI 2.1 Fault codes & diagnostics
65 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Gas
GC Number 47-077-74
Download the Baxi 424 COMBI 2.1 manual
PDF
Versions & GC numbers
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
Severity at a glance
Each cell = one fault code. Hover to identify. 65 Unrated
Which version do you have?
The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.
| GC number | Appliance (register name) | Produced |
|---|---|---|
| 47-077-74 | 424 COMBI 2.1 | 2024–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
Just want the most common Baxi 424 COMBI 2.1 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 65 documented codes
Tap any card for details
A.00.28
Solar temperature sensor is either removed or measures a temperature below range
A.00.29
Solar temperature sensor is either shorted or measures a temperature above range
A.00.34
Outdoor temperature sensor expected but not detected
A.02.06
Low system pressure in heating circuit
A.02.18
OBD error
A.02.36
Functional device disconnected
A.02.37
Passive functional device disconnected
A.02.45
Connection error
A.02.46
Device priority error
Showing 11–20 of 65
A.02.48
Unit function configuration error
A.02.49
Failed node initialisation
A.02.54
Open Therm bus power supply error
A.02.55
Incorrect or missing serial number
A.02.76
Internal memory reserved for full customisation of settings. No further changes can be made
E.00.04
Return temperature sensor disconnected
E.00.05
Return temperature sensor short circuited
E.00.16
DHW tank temperature sensor not connected
E.00.17
DHW tank temperature sensor short-circuited
E.00.20
The flue gas temperature sensor is not connected or measured a temperature below the range
Showing 21–30 of 65
E.00.21
The flue gas temperature sensor has short-circuited or measured a temperature above the range
E.01.04
Flame loss detected five times in 24 hours
E.01.12
Temperature measured by return sensor greater than flow temperature
E.01.17
No water circulation (permanent)
E.01.20
Maximum flue gas temperature reached
E.02.13
Total stoppage of the boiler (antifreeze function not active)
E.02.17
Permanent communication failure between gas valve and boiler PCB
E.02.35
Critical safety device disconnected
E.02.39
Minimum pressure not reached after 6 minutes of automatic filling
E.02.47
Connection to external device unsuccessful
Showing 31–40 of 65
E.04 | .54
Fault in gas valve control circuit
E.04.01
Flow temperature sensor short circuited
E.04.02
Flow temperature sensor disconnected
E.04.03
Maximum flow temperature exceeded or flow temperature sensor short circuited
E.04.08
Maximum safe temperature value reached
E.04.10
Burner failed to ignite after 4 attempts
E.04.12
Ignition failure - flame monitoring
E.04.13
Fan impeller blocked or maximum rpm exceeded
E.04.17
Fault in gas valve control circuit
E.04.18
The flow temperature is below the minimum temperature or the flow temperature sensor is not connected
Showing 41–50 of 65
E.04.23
Communication internal stoppage
E.04.29
Communication internal stoppage
E.04.54
Fault in gas valve control circuit
E.04.254
Fault in gas valve control circuit
H.00.42
Pressure sensor open/faulty
H.00.81
Room unit disconnected
H.01.00
Temporary communication failure between gas valve and boiler PCB.
H.01.05
Maximum temperature difference value between flow and return reached.
H.01.08
Flow temperature increase in heating mode too quick. Temporary stoppage of 10 minutes.
H.01.14
Maximum flow or return temperature value reached.
Showing 51–60 of 65
H.01.18
No water circulation (temporary).
H.01.21
Flow temperature increase during domestic hot water operation too fast
H.02.00
Reset in progress
H.02.02
Waiting for configuration settings to be entered (CN1,CN2).
H.02.03
Configuration settings (CN1,CN2) not entered correctly.
H.02.04
PCB settings cannot be read.
H.02.05
Setting memory not compatible with the boiler PCB type
H.02.07
Low pressure in heating circuit (permanently)
H.02.09
Partial stoppage of the boiler (antifreeze function active)
H.02.10
Total stoppage of the boiler (antifreeze function not active)
Showing 61–65 of 65
H.02.70
External unit heat recovery test failed
H.03.00
No identification data for boiler safety device.
H.03.02
Temporary flame loss
H.03.05
Power supply voltage too low
H.03.54
Temporary flame loss. Shutdown due to the power supply voltage being too low
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