BoilerFaultCodesThe 6 most common faults
01
C1 High Engineer
Your boiler is struggling to push air through its internal system effectively, which stops it from firing up safely.
Full guide for C102
C6 High Engineer
Your boiler has detected that the internal fan responsible for venting exhaust gases is spinning faster than it should, so it has safely shut down to prevent potential damage.
Full guide for C603
E2 High Engineer
Your boiler's temperature sensor is providing faulty information, causing the system to stop heating for safety reasons.
Full guide for E204
E9 High Engineer
Your boiler has detected that it is running too hot and has automatically shut down to prevent damage to the internal system.
Full guide for E905
EA High Engineer
Your boiler is trying to start but the flame is failing to light or stay lit, so it has shut itself off for safety.
Full guide for EA06
AC High Engineer
Your boiler's electronic control system is failing to communicate with its internal components, causing the system to shut down for safety.
Full guide for ACon the Worcester Bosch ZB 7 27 HE
Fan assemblyAir pressure switchFlue system componentsPrinted Circuit Board (PCB)NTC Temperature SensorWiring harness
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