Should a fault develop with your Worcester Bosch boiler, it will enter a safety lock-out mode, and fault code information will be generated as described below.
Worcester Bosch fault codes: locking errors
When a locking error occurs, the boiler display will flash a warning triangle and fault code. If you see the following fault codes on your Worcester Bosch boiler, the fault will need to be fixed (using our helpful guide below) and the boiler reset the boiler using the button on the control panel.
Some fixes will need to be completed by a Gas Safe registered engineer.
9A: HCM (Heat control module)
- Cause code: 362
- Possible cause: Incorrect HCM fitted
- Solution: You’ll need a gas safe registered engineer to fix this fault.
9U: HCM (Heat control module)
- Cause code: 233
- Possible cause: Problem with the code plug (faulty or not connected)
- Solution: You’ll need a gas safe registered engineer to fix this fault.
B7: Internal error
- Cause code: 257
- Reset type: Replace control board
- Solution: You’ll need a gas safe registered engineer to fix this fault.
C6: Fan problem
Cause code: 215
- Possible cause: Running too fast
- Solution: You’ll need a gas safe registered engineer to fix this fault.
Cause code: 216
- Possible cause: Running too slow
- Solution: You’ll need a gas safe registered engineer to fix this fault.
Cause code: 214
- Possible cause: Fan not running
- Solution: You’ll need a gas safe registered engineer to fix this fault.
Cause code: 217
- Possible cause: Fan not running or airflow blocked
- Solution: You’ll need a gas safe registered engineer to fix this fault.
D1: Return sensor error
Cause code: 240
- Possible cause: Sensor wet or damaged (the boiler will block for 300 seconds before this condition)
Cause code: 241
- Possible cause: Sensor disconnected or damaged (the boiler will block for 300 seconds before this condition)
D1: Return temperature too high
- Cause code: 286
- Possible cause: Boiler overheat
E2: Flow sensor short circuit
- Cause code: 222
- Possible cause: Flow sensor shorted or damaged
Cause code: 223
- Possible cause: Flow sensor disconnected or damaged
E5: Flow temperature too high
- Cause code: 218
- Possible cause: Primary flow sensor overheated
E5: Primary flow sensor has exceeded 110°C
- Cause code: 332
- Possible cause: Primary flow sensor overheated
E9: Safety sensor temperature too high
- Cause code: 219
- Possible cause: The main heat exchanger has overheated. Maximum temperature 105 °C
E9: Safety sensor short circuit
- Cause code: 220
- Possible cause: Maximum temperature sensor on the main heat exchanger has failed
E9: Safety sensor open circuit
Cause code: 221
Possible cause: Maximum temperature sensor on the main heat exchanger has not been recognised
E9: Max temperature thermostat activated
- Cause code: 224
- Possible cause: Flue gas thermostat overheat
EA: No flame detected after ignition
- Cause code: 227
- Possible cause: Failure of four ignition attempts. The boiler waits 30 seconds before another attempt is made
EA: Loss of flame signal during operation
- Cause code: 229
- Possible cause: An established flame has been extinguished. This could be caused by:
- Moisture in the sump, due to a blocked sump/condensate trap
- A strong wind into the flue
EA: Gas valve error
- Cause code: 234
- Possible cause: Gas valve coil disconnected
EA: Ignition timing error
- Cause code: 261
- Possible cause: Flame not established during the first 4 seconds ignition period
EA: Too many short burner starts without confirmation
- Cause code: 338
- Possible cause: There is an error where the pump is not detecting water – check pressure gauge and repressurise to 1 bar
Worcester Bosch fault codes: blocking errors
With a blocking error, the boiler will stop operating and won’t display a fault code. You can still access the cause code in the info menu by pressing the spanner/return button, which should give you a better idea of what’s going on.
The condition will clear automatically when the associated fault clears e.g. waiting for an area to cool. In some cases, a blocking error has a defined time duration prior to changing to a locking condition.
A1: Pump stuck or running in air
- Cause code: 281
- Possible cause: Little or no water in the system – check pressure gauge and repressurise to 1 bar
C1: Airflow stopped during operation
- Cause code: 264
- Possible cause: Fan has stopped
EA: No ionisation detected after ignition
- Cause code: 227
- Possible cause: No flame is detected. The boiler will block during 4 attempts before going to Locking fault
EF: Central heating, boil detect – Large delta T despite minimum burner
- Cause code: 349
- Possible cause: The boiler is operating at minimum burner load and there is a greater than 18 °C Flow & Return temperature difference
No code: Safety or flow temperature rises too fast
- Cause code: 212
- Possible cause: Air lock or reduced water content – check pressure gauge and repressurise to 1 bar
No code: Temperature difference between supply and return exceeding limit
- Cause code: 213
- Possible cause: Air lock or reduced water content – check pressure gauge and repressurise to 1 bar
No code: No temperature rise after burner starts
- Cause code: 260
- Possible cause: Sensor disconnected or no water content – check pressure gauge and repressurise to 1 bar
Maintenance codes
These are displayed with the letter H followed by a number. The code advises of a situation that will need some attention but is not a fault that will stop the boiler from functioning. Some of the common ones are listed:
H11
Hot water outlet sensor defect. Hot water can still be delivered but with less control.
H13
This can mean that your boiler is due for a service. It shows when an internal timer expires in the boiler to remind you about your annual boiler service. You can also disable this reminder by finding the appropriate settings in your boiler manual.
Boiler repairs from HomeServe
Experiencing problems with your Worcester Bosch boiler? Our expert repairs team are on hand to diagnose the issue and will aim to get things working again in no time.
Alternatively, if you’re looking for a new boiler, we’re working together with BOXT, one of the largest boiler installation companies in the UK, to help you find the best boiler for your home.
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