BoilerFaultCodesThe 6 most common faults
01
LOCK OUT High DIY-safe
Your boiler has stopped working for safety reasons and needs a manual reset to attempt to start up again.
What to try first
Turn your boiler thermostat dial fully anti-clockwise to the reset position and hold it there for a few seconds.Turn the dial clockwise back to your desired temperature setting.Wait a few minutes to see if the boiler ignites and the flame icon appears.
02
FLAME FAILURE NEON High Engineer
Your boiler has stopped working because it cannot light the gas burner or keep it burning.
Full guide for FLAME FAILURE NEON03
OVERHEAT NEON High Engineer
Your boiler has automatically shut itself down because it detected that it is getting too hot, likely due to a circulation problem.
Full guide for OVERHEAT NEON04
Neon L2 High Engineer
Your boiler is struggling to correctly read or communicate the temperature of the water, so it has safely paused operation to prevent overheating.
Full guide for Neon L205
Neon L3 High Engineer
Your boiler is struggling to clear exhaust fumes because it cannot confirm that the internal fan is moving air properly, preventing it from lighting safely.
Full guide for Neon L306
Neon L4 High Engineer
Your boiler is failing to detect a flame, so it has purposefully shut itself down to prevent a gas leak.
Full guide for Neon L4on the Halstead Hero
Ignition electrodeGas valvePrinted circuit board (PCB)Burner assemblyPCBOverheat thermostat
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 Halstead 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