Boiler Fault Code F5 Or L5

Also written as F5ORL5 — same fault.

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

Fault code F5 Or L5 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 lost the ability to accurately measure the temperature of the water returning to it, so it has safely shut down to prevent overheating. (As reported on Ideal Logic Combi C24 C30 C35)