BoilerFaultCodesThe 4 most common faults
01
Neon 1 High Engineer
Your boiler is not detecting the correct electrical power supply, which is usually caused by a blown internal fuse or a power cut.
Full guide for Neon 102
Neon 3 High Engineer
Your boiler is failing to detect the correct airflow needed to safely burn gas and clear exhaust gases.
Full guide for Neon 303
Neon 4 High Engineer
Your boiler has failed to light or stay safely lit, so it has locked out to prevent any unburnt gas from building up.
Full guide for Neon 404
Neon 2 Emergency Engineer
Your boiler has automatically shut down because it has detected dangerously high internal temperatures.
Full guide for Neon 2on the Saunier Duval Xeon 40ff
PCB fusePrinted Circuit Board (PCB)Power supply cableAir pressure switchFlue fanVenturi
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
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