BoilerFaultCodesThe 4 most common faults
01
A1 High Engineer
Your boiler is struggling because the internal water pump is stuck or cannot circulate water properly, preventing your heating and hot water from working.
Full guide for A102
C1 High Engineer
Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.
Full guide for C103
E01 High Engineer
Your boiler is struggling to accurately measure the temperature of the water, which means it has safely shut down to prevent overheating.
Full guide for E0104
AC High Engineer
Your boiler's computer is having trouble communicating with an internal part, which prevents the system from starting up safely.
Full guide for ACon the Worcester Bosch 28 Cdi RSF
Circulation pumpPump headFan assemblyPrinted Circuit Board (PCB)Venturi tubeHot water NTC sensor
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