BoilerFaultCodes 3 0 4 Medium
Boiler Fault Code 3 0 4
Also written as 304 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 3 0 4 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 been manually reset too many times in a short period, so it has locked itself out to prevent potential damage. (As reported on Ariston HS Premium)
Pick your boiler brand for the 3 0 4 fix
Source
Information for the 3 0 4 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