BoilerFaultCodesThe 6 most common faults
01
Lockout High Engineer
Your boiler has stopped working because it failed to start after three attempts, which is often caused by an interruption to the gas supply or a trapped air pocket.
Full guide for Lockout02
Mains ON Only High Engineer
Your boiler has stopped working and is showing a fault light, meaning it has detected an internal error that has forced it to shut down for safety.
Full guide for Mains ON Only03
FLAME Detected High Engineer
Your boiler has detected a flame when it should not be lit, which means the system is currently trying to reset itself to ensure safe operation.
Full guide for FLAME Detected04
Blocking High Engineer
Your boiler has detected an internal issue with its airflow system or electrical supply, causing it to shut down for safety reasons.
Full guide for Blocking05
Overheat condition High Engineer
Your boiler has switched itself off because it has detected an unsafe rise in temperature and needs a manual reset to start working again.
Full guide for Overheat condition06
red light flashing High Engineer
Your boiler has failed to start after several attempts because it cannot detect a flame, so it has turned itself off for safety.
Full guide for red light flashingon the Potterton Puma 80/100
Ignition electrodeGas valvePrinted Circuit BoardPrinted Circuit Board (PCB)DHW Flow SwitchFan Assembly
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 Potterton 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