6 nn Low

Keston 6 nn Fault Code

Also written as 6NN — same fault.

The Keston 6 nn fault code means: your boiler has successfully reached the desired temperature and has automatically switched off to save energy, so there is no fault at all.. It appears on 3 Keston models 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: Burner is off because the boiler is up to temperature

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Keston models that show the 6 nn fault code

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

Source

Keston 6 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 7 July 2026