How much does it cost to fix boiler error code 91?

Typical repair cost for the boiler 91 fault is £120-200 including labour.

91 Medium

Boiler Fault Code 91

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code 91 appears across 6 boiler brands and 15 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 grime or debris is building up inside the system and requires a professional service to ensure it continues to run safely and efficiently. (As reported on Vokera Linea One)

Pick your boiler brand for the 91 fix

Alpha 91 4 models Biasi 91 4 models ECA 91 1 model Keston 91 1 model Viessmann 91 4 models Vokera 91 1 model

Source

Information for the 91 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