BoilerFaultCodesThe 6 most common faults
01
Neon 1 High DIY-safe
Your boiler has no electricity flowing to it, meaning it cannot start up to provide heating or hot water.
What to try first
Check the main fuse spur switch next to the boiler is turned onCheck your household consumer unit to ensure the boiler circuit breaker has not trippedCheck that the plug, if present, is pushed firmly into the socket
02
Neon 2 High Engineer
Your boiler has stopped working because a safety sensor has triggered a shutdown to prevent it from getting too hot.
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 igniting or staying lit.
Full guide for Neon 304
Neon 4 High Engineer
Your boiler has stopped working because the main control panel is failing to send electrical power to the internal gas valve to start the heating process.
Full guide for Neon 405
Neon 1 lit High Engineer
Your boiler is failing to detect an electrical power supply, meaning it cannot switch on or operate your heating and hot water.
Full guide for Neon 1 lit06
Neon 2 lit High Engineer
Your boiler has stopped heating because it has detected a heat safety issue and automatically shut down to prevent damage.
Full guide for Neon 2 liton the Saunier Duval Xeon 120 FF
Fused spurPCBWiring harnessOverheat thermostatLimit switchAir pressure switch
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