BoilerFaultCodes 4 03 High
Boiler Fault Code 4 03
Also written as 403 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 4 03 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's internal computer is experiencing a critical error and can no longer control the system, meaning your heating and hot water will not work. (As reported on Vokera Eclipse)
Pick your boiler brand for the 4 03 fix
Source
Information for the 4 03 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 7 July 2026