BoilerFaultCodes 4 AT High
Boiler Fault Code 4 AT
Also written as 4AT — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 4 AT 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 stopped working because a safety fuse on the main internal computer board has blown, cutting off electrical power to the system. (As reported on Baxi Barcelona)
Pick your boiler brand for the 4 AT fix
Source
Information for the 4 AT 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