0 nn Low

Boiler Fault Code 0 nn

Also written as 0NN — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code 0 nn 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 currently in standby mode because it is not receiving a signal from your thermostat or timer to provide heating or hot water. (As reported on Keston C90 / C110)

Pick your boiler brand for the 0 nn fix

Keston 0 nn 1 model

Source

Information for the 0 nn 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