BoilerFaultCodesKeston F9 Fault Code
The Keston F9 fault code means: your boiler's internal computer has encountered a critical error and cannot communicate with the rest of the system.. It appears on 8 Keston models in our database.
Technical description: Printed circuit board (PCB) Fault
What causes the Keston F9 fault?
This fault occurs when the boiler's central control board suffers an internal hardware failure or loses the ability to send signals to other components. It is often caused by a surge in the electrical supply, moisture ingress, or simply the natural degradation of the solder joints and microprocessors over time. The system shuts down as a safety precaution because it can no longer monitor the boiler's operation accurately.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Keston models that show the F9 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston F9 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