BoilerFaultCodesBaxi D neon flashing Fault Code
Also written as DNEONFLASHING — same fault.
The Baxi D neon flashing fault code means: your boiler has detected that it is running too hot or that the exhaust system is blocked, so it has safely shut itself down to prevent damage.. It appears on 2 Baxi models in our database.
Technical description: Overheat thermostat or flue thermostat tripped; investigation required in section D
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Baxi models that show the D neon flashing fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi D neon flashing fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026