BoilerFaultCodes F 4 L 4 High
Boiler Fault Code F 4 L 4
Also written as F4L4 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F 4 L 4 appears across 1 boiler brand and 1 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 internal sensor that monitors the temperature of the water as it leaves the unit, causing it to shut down as a precaution. (As reported on Ideal Instinct2 24)
Pick your boiler brand for the F 4 L 4 fix
Source
Information for the F 4 L 4 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