BoilerFaultCodesKeston 7 nn Fault Code
Also written as 7NN — same fault.
The Keston 7 nn fault code means: your boiler is simply performing a routine two-minute cooling cycle after finishing its heating task, and this is a normal part of how it protects itself.. It appears on 3 Keston models in our database.
Technical description: Boiler pump is in Central Heating 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 7 nn fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston 7 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