Boiler Fault Code 5 04

Also written as 504 — same fault.

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

Fault code 5 04 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 is struggling to keep the flame lit correctly, meaning it will likely shut down for safety reasons to prevent incomplete combustion. (As reported on Ariston Egis)