How much does it cost to fix boiler error code 9 nn?

Typical repair cost for the boiler 9 nn fault is £150-350 including labour.

9 nn High

Boiler Fault Code 9 nn

Also written as 9NN — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code 9 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 has detected an internal error it does not recognise and has shut itself down as a safety precaution. (As reported on Keston C90 / C110)

Pick your boiler brand for the 9 nn fix

Keston 9 nn 1 model

Source

Information for the 9 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