BoilerFaultCodes F9/L9 High
Boiler Fault Code F9/L9
Also written as F9L9 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F9/L9 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's main control computer is experiencing a critical error and is unable to communicate properly, meaning your heating and hot water will not work. (As reported on Ideal Atlantic Combi)
Pick your boiler brand for the F9/L9 fix
Source
Information for the F9/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