BoilerFaultCodes F9 or L9 High
Boiler Fault Code F9 or L9
Also written as F9ORL9 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F9 or L9 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's internal computer has suffered a critical failure and can no longer control the heating system, meaning the unit will not operate. (As reported on Ideal Atlantic Combi)
Pick your boiler brand for the F9 or L9 fix
Source
Information for the F9 or L9 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