Boiler Fault Code 3 04

Also written as 304 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 3 04 appears across 1 boiler brand and 13 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 reset button has been pressed too many times in a short period, which has triggered a built-in safety lockout to prevent potential damage to the electronic control board. (As reported on Ariston E-Combi One 30)