Worcester Bosch Boiler Fault Codes
Worcester Bosch Boiler Fault Codes
If your Worcester Bosch boiler develops a fault, it will automatically enter a lock out mode for safety. It will then display a specific fault code, which will indicate the problem and help to find a solution.

Types of Common Worcester Bosch Fault Errors
Worcester Bosch Boiler Locking Errors
9A
HCM (Heat Control Module)Cause Code – 362
Reset Type – Reset button
Possible Cause – Incorrect HCM fitted
9U
HCM (Heat Control Module)Cause Code – 233
Reset Type – Reset button
Possible Cause – Problem with the code plug, either faulty or not connected.
B7
Internal ErrorCause Code – 257
Possible Cause – Control board needs replacing.
C6
Fan ProblemCause Code – 215/216
Reset Type – Reset button
Possible Cause – The fan is running too fast (215) or too slow (216).
C7
Fan ProblemCause Code – 214
Reset Type – Reset button
Possible Cause – The fan is not running.
C7
No Airflow After a Defined Period of TimeCause Code – 217
Reset Type – Reset button
Possible Cause – Fan not running or the airflow has been blocked.
D1
Return Sensor ErrorCause Code – 240
Reset Type – Reset button
Possible Cause – The sensor has become wet or damaged, which results in the boiler blocking for 300 seconds beforehand.
D1
Return Sensor ErrorCause Code – 241
Reset Type – Reset button
Possible Cause – The sensor has been disconnected or damaged, which results in the boiler blocking for 300 seconds beforehand.
D1
Return Temperature Too HighCause Code – 286
Reset Type – Reset button
Possible Cause – Boiler is overheating.
E2
Flow Sensor Short CircuitCause code – 222
Reset Type – Reset button
Possible Cause – Flow sensor has become shorted or damaged.
E2
Flow Sensor Open CircuitCause Code – 223
Reset Type – Reset button
Possible Cause – Flow sensor has become disconnected or damaged.
E5
Flow Temperature Too HighCause Code – 218
Reset Type – Reset button
Possible Cause – Primary flow sensor is overheating.
E5
Primary Flow Sensor Has Exceeded 110°CCause Code – 332
Reset Type – Reset button
Possible Cause – Primary flow sensor is overheating.
E9
Safety Sensor Temperature Too HighCause Code – 219
Reset Type – Reset button
Possible Cause – The main heat exchanger has overheated and the maximum temperature has reached 105°C.
E9
Safety Sensor Short CircuitCause Code – 220
Reset Type – Reset button
Possible Cause – The maximum temperature sensor on the main heat exchanger has failed.
E9
Safety Sensor Open CircuitCause Code – 221
Reset Type – Reset button
Possible Cause – The maximum temperature sensor on the main heat exchanger has not been recognised.
E9
Max Temperature Thermostat ActivatedCause Code – 224
Reset Type – Reset button
Possible Cause – The flue gas thermostat is overheating.
EA
No Flame Detected After IgnitionCause Code – 227
Reset Type – Reset button
Possible Cause – The ignition has failed four times.
EA
Loss of Flame Signal During OperationCause Code – 229
Reset Type – Reset button
Possible Cause – The established flame has been extinguished, which could be due to moisture in the sump or a strong wind into the flue.
EA
Gas Valve ErrorCause Code – 234
Reset Type – Reset button
Possible Cause – The gas valve coil has been disconnected.
EA
Ignition Timing ErrorCause Code – 261
Reset Type – Reset button
Possible Cause – The flame has not been established during the first four seconds of the ignition period.
EA
Too Many Short Burner Starts Without ConfirmationCause Code – 338
Reset Type – Reset button
Possible Cause – The pump is not detecting water, which can be resolved by checking the pressure gauge and repressurising to one bar.
Worcester Bosch Boiler Blocking Errors
A1
Pump Stuck or Running on AirCause Code – 281
Possible Cause – There’s little/no water in the system, which can be resolved by checking the pressure gauge and repressurising to one bar.
C1
Airflow Stopped During OperationCause Code – 264
Possible Cause – The fan has stopped working.
EA
No Ionisation Detected After IgnitionCause Code – 227
Possible Cause – There’s no flame detected, which will lead to the boiler blocking during four attempts before becoming a locking fault.
EF
Central Heating Boiler Defect (large delta T, despite minimum burner)Cause Code – 349
Possible Cause – The boiler is operating at minimum burner load, whilst there is also a flow and return temperature difference of more than 18°C.
No Code
Safety or Flow Temperature Rises Too FastCause Code – 212
Possible Cause – The air lock or reduced water content has a fault, which can be resolved by checking the pressure gauge and repressurising to one bar.
No Code
The Limit Has Exceeded on the Temperature Difference Between Supply and ReturnCause Code – 213
Possible Cause – The air lock or reduced water content has a fault, which can be resolved by checking the pressure gauge and repressurising to one bar.
No Code
No Temperature Rise After Burner StartsCause Code – 260
Possible Cause – The sensor has become disconnected or there’s no water content, which can be resolved by checking the pressure gauge and repressurising to one bar.
Any questions?
If you are looking for a heating engineer within the Milton Keynes area for anything from boiler installations to fixing a tap, or would like some friendly advice please call Mitch directly today on 01908 034194
Areas we cover
- Aylesbury
- Bedford
- Leighton Buzzard
- Northampton
- Olney
- Towcester
- Woburn Sands
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