Boiler Fault Code C1 11

Also written as C111 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code C1 11 appears across 1 boiler brand 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 water inside has become dangerously hot and has shut itself down to prevent damage or safety issues. (As reported on Atag S 25CR)