How much does it cost to fix boiler error code 66?

Typical repair cost for the boiler 66 fault is £120-200 including labour.

66 Low

Boiler Fault Code 66

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code 66 appears across 2 boiler brands and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is receiving conflicting or faulty signals from an outdoor temperature sensor, which may cause your heating to run less efficiently or turn off unexpectedly. (As reported on Sime Dewy 30/50 HE WM)

Pick your boiler brand for the 66 fix

Gledhill 66 1 model Sime 66 4 models

Source

Information for the 66 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