BoilerFaultCodes 43 mm Low
Boiler Fault Code 43 mm
Also written as 43MM — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 43 mm 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 This is a technical configuration setting for your boiler's flue rather than a system fault, indicating the specific size of the air restrictor plate required for your flue pipe setup. (As reported on Ferroli F24b)
Pick your boiler brand for the 43 mm fix
Source
Information for the 43 mm 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