BoilerFaultCodes 266 High
Boiler Fault Code 266
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 266 appears across 2 boiler brands and 4 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 internal fan responsible for safely clearing exhaust gases is not spinning at the correct speed. (As reported on Navien NCM 1130HH)
Pick your boiler brand for the 266 fix
Source
Information for the 266 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 31 August 2026