BoilerFaultCodesThe 6 most common faults
01
HE High Engineer
Your boiler's computer system is experiencing a major internal processing error and cannot safely manage the heating process.
Full guide for HE02
L9 High Engineer
Your boiler has detected that the gases leaving through the flue are getting too hot, so it has automatically shut itself down to prevent damage.
Full guide for L903
H9/L9 High Engineer
Your boiler has shut down because the internal gases have become too hot, causing the system to lock out for safety until it cools down.
Full guide for H9/L904
L-F High Engineer
Your boiler is failing to light the internal flame or keep it burning, which means your heating and hot water have stopped working.
Full guide for L-F05
H-E High Engineer
Your boiler’s internal computer has encountered a critical communication error and can no longer control the heating or hot water functions.
Full guide for H-E06
H9 Emergency Engineer
Your boiler has detected that the gases being sent out through your flue are reaching dangerously high temperatures and has shut itself down to prevent damage or fire risk.
Full guide for H9on the Ideal Icos
Printed Circuit Board (PCB)Heat exchangerNTC thermistorFlue gas sensorHeat ExchangerFlue Thermistor
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 Ideal 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