BoilerFaultCodesThe 6 most common faults
01
F1 High Engineer
Your boiler is trying to start but cannot get a flame going, so it has turned itself off for safety.
Full guide for F102
F4 High Engineer
Your boiler is failing to stay lit, which means it has safely shut itself down to prevent a gas buildup.
Full guide for F403
F5 High Engineer
Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage.
Full guide for F504
F6 High Engineer
Your boiler is currently unable to read the temperature of the water being sent to your radiators, so it has stopped working to prevent potential overheating.
Full guide for F605
F7 High Engineer
Your boiler is struggling to accurately measure the temperature of your hot water, which means it will likely stop producing hot water until the faulty sensor is replaced.
Full guide for F706
F10 High Engineer
Your boiler is struggling to accurately measure the temperature of the water returning to it from your radiators, so it has shut down to prevent potential damage.
Full guide for F10on the Glow-worm CXi
Ignition electrodeGas valvePrinted Circuit Board (PCB)Flame sensorPCBNTC 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 Glow-worm 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