BoilerFaultCodes ALL03 Emergency
Boiler Fault Code ALL03
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code ALL03 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 too much water inside it, causing the internal pressure to rise to an unsafe level. (As reported on Sime iQE Simplicity 20T)
Pick your boiler brand for the ALL03 fix
Source
Information for the ALL03 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