BoilerFaultCodes L4 or F4 High
Boiler Fault Code L4 or F4
Also written as L4ORF4 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code L4 or F4 appears across 2 boiler brands and 7 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's temperature-sensing component is malfunctioning, which prevents it from safely controlling the heat, so it has turned itself off to prevent overheating. (As reported on Ideal Logic Code Combi ESP1)
Pick your boiler brand for the L4 or F4 fix
Source
Information for the L4 or F4 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 7 July 2026