BoilerFaultCodesThe 6 most common faults
01
Blue light: Off / Lockout: Off High DIY-safe
Your boiler has completely lost all electrical power, meaning it cannot operate your heating or hot water at all.
What to try first
Check your home's fuse box or consumer unit to see if the RCD or boiler circuit breaker has tripped.Verify the fused spur switch located near the boiler is turned on.Ensure the plug or connection at the fused spur is secure and the fuse inside the spur hasn't blown.
02
lock-out High Engineer
Your boiler is failing to light the flame, so it has safely shut itself down to prevent a gas leak.
Full guide for lock-out03
LOCKOUT High Engineer
Your boiler has stopped working because it cannot light its internal flame, which means your heating and hot water have switched off for safety.
Full guide for LOCKOUT04
Pump does not run High Engineer
Your boiler is failing to circulate water through your radiators or hot water tank, meaning your home will not be able to heat up.
Full guide for Pump does not run05
Fan does not run High Engineer
Your boiler has stopped working because it cannot properly move the air and fumes required for safe operation.
Full guide for Fan does not run06
Electrode does not spark High Engineer
Your boiler is failing to ignite because it cannot create the spark needed to light the flame.
Full guide for Electrode does not sparkon the Worcester Bosch Greenstar 15i System
External fusePrinted Circuit Board (PCB)TransformerIgnition electrodeGas valveIgnition lead
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