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 1 boiler brand and 8 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 that water is either not moving through the system properly or a temperature sensor is giving a faulty reading, causing the unit to shut down for safety. (As reported on Ideal Vogue)
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 27 April 2026