BoilerFaultCodesSaunier Duval Neon 4 NOT lit Fault Code
Also written as NEON4NOTLIT — same fault.
The Saunier Duval Neon 4 NOT lit fault code means: your boiler is failing to light the burner, meaning it cannot produce heat or hot water because it has detected an issue with the ignition process.. It appears on 2 Saunier Duval models in our database.
Technical description: Ignition, pilot or flame proving fault
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Saunier Duval models that show the Neon 4 NOT lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval Neon 4 NOT lit fault code information on this page is sourced and cross-checked against the official Saunier Duval service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026