BoilerFaultCodes 40°C neon flashing High
Boiler Fault Code 40°C neon flashing
Also written as 40CNEONFLASHING — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 40°C neon flashing 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 is failing to detect the flow of water needed to fire up the heating, meaning it cannot start the system. (As reported on Potterton Performa 24)
Pick your boiler brand for the 40°C neon flashing fix
Source
Information for the 40°C neon flashing 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