BoilerFaultCodes 3 05 High
Boiler Fault Code 3 05
Also written as 305 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 3 05 appears across 1 boiler brand and 14 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has detected an internal communication error with its main control unit, meaning it has shut down as a safety precaution to prevent incorrect operation. (As reported on Ariston Clas System 28)
Pick your boiler brand for the 3 05 fix
Source
Information for the 3 05 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