BoilerFaultCodes 303 High
Boiler Fault Code 303
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 303 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 main control board has detected an internal electronic error and has shut down as a safety precaution. (As reported on Ariston Alteas One)
Pick your boiler brand for the 303 fix
Source
Information for the 303 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