BoilerFaultCodesThe 6 most common faults
01
Neon 1 High DIY-safe
Your boiler is not receiving any electricity, which means it has completely shut down and cannot heat your home or water.
What to try first
Check that the boiler power switch or fused spur next to the unit is turned on.Check your home's main consumer unit (fuse box) to see if a trip switch or fuse has blown.Plug a small appliance into the wall socket used by the boiler to confirm that the socket itself is providing power.
02
Neon 1 lit High DIY-safe
Your boiler is currently receiving no electrical power, meaning it cannot operate your heating or hot water.
What to try first
Check that the fused spur switch for the boiler is in the ON position.Inspect your home's fuse box or consumer unit to see if the circuit breaker for the heating system has tripped.Ensure the plug or connection at the boiler isolation switch is secure and the fuse in the spur hasn't blown.
03
Neon 2 High Engineer
Your boiler has stopped working because a safety switch has detected that the unit became too hot and triggered a shutdown.
Full guide for Neon 204
Neon 3 High Engineer
Your boiler has detected an issue with its internal air supply system, which is preventing it from safely starting up the burner.
Full guide for Neon 305
Neon 4 High Engineer
Your boiler has stopped working because it cannot detect or signal that it is ready to fire up, likely due to an internal electrical communication fault.
Full guide for Neon 406
Neon 1 NOT lit High Engineer
Your boiler is not receiving any electricity, which means it cannot power up to provide heating or hot water.
Full guide for Neon 1 NOT liton the Saunier Duval Xeon 30ff
Printed Circuit Board (PCB)FusesPower cablePrinted Circuit BoardExternal fuseInternal wiring harness
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 Saunier Duval 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