BoilerFaultCodes 5 nn Low
Boiler Fault Code 5 nn
Also written as 5NN — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 5 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 recalibrating its internal settings and should return to normal operation automatically once the process is complete. (As reported on Keston C90 / C110)
Pick your boiler brand for the 5 nn fix
Source
Information for the 5 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