BoilerFaultCodesThe 6 most common faults
01
A7 High Engineer
Your boiler has lost the ability to accurately measure the temperature of your hot water, so it has shut down to prevent overheating.
Full guide for A702
A8 High Engineer
Your boiler has lost the ability for its internal parts to 'talk' to each other, meaning it has safely shut down until the connection is restored.
Full guide for A803
C1 High Engineer
Your boiler is struggling to breathe properly because its internal ventilation fan is not spinning fast enough to clear fumes safely.
Full guide for C104
C6 High Engineer
Your boiler has detected that the internal fan is spinning faster than it should, so it has safely shut itself down to prevent any issues.
Full guide for C605
E2 High Engineer
Your boiler's internal thermometer is not sending a proper signal, so the system has shut down its heating and hot water functions to avoid overheating.
Full guide for E206
EA High Engineer
Your boiler is trying to start but the flame is failing to ignite or stay lit, so it has shut down as a safety precaution.
Full guide for EAon the Worcester Bosch Greenstar System
NTC Temperature SensorWiring harnessPrinted Circuit Board (PCB)Fan assemblyIgnition electrodeGas valve
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Worcester Bosch shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue
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