BoilerFaultCodes 6 04 Emergency
Boiler Fault Code 6 04
Also written as 604 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 6 04 appears across 1 boiler brand and 9 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 that the internal fan responsible for safely removing exhaust gases is not spinning fast enough, causing the system to stop for safety reasons. (As reported on Ariston Clas System 28)
Pick your boiler brand for the 6 04 fix
Source
Information for the 6 04 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