BoilerFaultCodes 100mm Emergency
Boiler Fault Code 100mm
Also written as 100MM — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 100mm 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 detected that the flue pipe is set to the wrong size or is incorrectly configured for your specific model, which prevents it from safely venting exhaust gases. (As reported on Main Combi 24)
Pick your boiler brand for the 100mm fix
Source
Information for the 100mm 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