BoilerFaultCodesSaunier Duval Neon 2 NOT lit Fault Code
Also written as NEON2NOTLIT — same fault.
The Saunier Duval Neon 2 NOT lit fault code means: your boiler has automatically shut itself down because it detected that it is getting too hot, likely due to a flow restriction or a failing safety sensor.. It appears on 2 Saunier Duval models in our database.
Technical description: Overheat cut off device tripped or thermostat, overheat cut off device faulty
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 2 NOT lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval Neon 2 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