BoilerFaultCodesThe 6 most common faults
01
Ignition Lockout High Engineer
Your boiler has failed to light because it cannot detect a flame, so it has safely shut itself down to prevent any gas buildup.
Full guide for Ignition Lockout02
No Switched Live High Engineer
Your boiler has lost its electrical signal, meaning it cannot receive the command to turn on and provide heating or hot water.
Full guide for No Switched Live03
Lights: Off Off Off High Engineer
Your boiler has completely lost power and is unable to turn on because it is not receiving any electricity.
Full guide for Lights: Off Off Off04
Lights: On Flash Flash High Engineer
Your boiler has detected that it is running without enough water inside, which means it has safely shut itself down to prevent damage to its internal parts.
Full guide for Lights: On Flash Flash05
Lights: Flash On Flash High Engineer
Your boiler's internal computer has developed an electronic fault and is no longer able to communicate with the rest of the system to turn on your heating.
Full guide for Lights: Flash On Flash06
Lights: On On Flash High Engineer
Your boiler's electronic command center has encountered a serious internal error and can no longer control the heating system safely.
Full guide for Lights: On On Flashon the Potterton Promax Heat Only
Ignition electrodeGas valvePCBIgnition leadControl PCBInternal Fuse
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