BoilerFaultCodes Neon D NOT illuminated High
Boiler Fault Code Neon D NOT illuminated
Also written as NEONDNOTILLUMINATED — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Neon D NOT illuminated appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has no power, meaning it cannot start up to provide heating or hot water because it is not receiving any electricity. (As reported on Alpha CD C)
Pick your boiler brand for the Neon D NOT illuminated fix
Source
Information for the Neon D NOT illuminated fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026