BoilerFaultCodes 1-C4 Low
Boiler Fault Code 1-C4
Also written as 1C4 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 1-C4 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 is displaying the current outdoor temperature because an external weather sensor is connected, which is a normal status reading rather than a breakdown. (As reported on Worcester Bosch Greenstar 8000 Life/Style)
Pick your boiler brand for the 1-C4 fix
Source
Information for the 1-C4 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 27 April 2026