BoilerFaultCodesThe 4 most common faults
01
IGNITION LOCKOUT High Engineer
Your boiler has failed to light because it cannot detect a proper gas supply or flame, meaning it has temporarily shut itself down for safety.
Full guide for IGNITION LOCKOUT02
OVERHEAT LOCKOUT High Engineer
Your boiler has automatically shut down because the internal water temperature became too high, acting as a crucial safety measure to prevent damage.
Full guide for OVERHEAT LOCKOUT03
FAN LOCKOUT High Engineer
Your boiler has temporarily stopped working because it has detected an issue with the internal fan that safely removes exhaust gases.
Full guide for FAN LOCKOUT04
THERMISTOR High Engineer
Your boiler's temperature sensor is failing, so it cannot accurately read how hot the water is and has safely shut down to prevent overheating.
Full guide for THERMISTORon the Main 12 Heat ErP range
Gas valveIgnition electrodePCBHigh limit thermostatNTC thermistorFan 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 Main 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
Boiler cover options
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
Approved partner
Get a quote →
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Affiliate links. We may earn a commission at no extra cost to you.