BoilerFaultCodesThe 6 most common faults
01
C1 High Engineer
Your boiler has detected that the internal fan is moving too slowly to safely clear exhaust gases, so it has stopped working to keep your home safe.
Full guide for C102
C4 High Engineer
Your boiler's internal fan is stuck running continuously, which prevents the system from starting its normal cycle and will eventually cause further components to fail.
Full guide for C403
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 damage.
Full guide for C604
d3 High Engineer
Your boiler has stopped working because a safety link inside the unit has either come loose or a connected external safety device has shut the system down.
Full guide for d305
E2 High Engineer
Your boiler has stopped working because a sensor that measures the water temperature is broken or has a faulty connection.
Full guide for E206
E9 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for E9on the Worcester Bosch R30 HE Plus
Fan assemblyPrinted Circuit Board (PCB)Printed circuit board (PCB)Link plugExternal overheat thermostatWiring 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