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 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 203
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 304
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 405
Neon 2 lit High Engineer
Your boiler has stopped working because a safety sensor has tripped, likely due to the system getting too hot.
Full guide for Neon 2 lit06
Neon 3 lit High Engineer
Your boiler is failing to detect the airflow needed for safe operation, likely due to an internal electrical connection issue or a faulty main control board.
Full guide for Neon 3 liton the Saunier Duval Xeon 30ff
Printed Circuit Board (PCB)FusesPower cableOverheat thermostatLimit switchPrinted circuit board (PCB)
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