8 nn Low

Keston 8 nn Fault Code

Also written as 8NN — same fault.

The Keston 8 nn fault code means: your boiler is currently just finishing a standard cooling-down cycle after producing hot water and is operating exactly as it should.. 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: Boiler pump is in DHW overrun mode (2 mins)

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 8 nn fault code

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

Source

Keston 8 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