BoilerFaultCodes A03 High
Boiler Fault Code A03
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code A03 appears across 3 boiler brands and 26 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has switched itself off because it has become too hot internally, likely due to a lack of water or a blockage preventing water from moving around the system. (As reported on Potterton Powermax HE)
Pick your boiler brand for the A03 fix
Source
Information for the A03 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