0 nn Low

Keston 0 nn Fault Code

Also written as 0NN — same fault.

The Keston 0 nn fault code means: 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.. It appears on 1 Keston model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Module in standby as no heat request from either zone

DIY fix possible

Check that your heating timer or programme is set to 'On'Turn up the temperature on your room thermostat to see if the boiler fires upEnsure the boiler's own internal temperature or mode settings are currently active

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Keston models that show the 0 nn fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Keston 0 nn fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.

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