BoilerFaultCodes F04 L04 High
Boiler Fault Code F04 L04
Also written as F04L04 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F04 L04 appears across 1 boiler brand and 3 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 a problem with the sensor that monitors the temperature of the water leaving the unit, usually causing the system to shut down as a safety precaution. (As reported on Ideal Logic Code Combi ESP1)
Pick your boiler brand for the F04 L04 fix
Source
Information for the F04 L04 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