BoilerFaultCodesKeston F6 Fault Code
The Keston F6 fault code means: your boiler has lost communication with the sensor that measures the temperature outside, which may cause your heating to be less efficient or run at the wrong temperature.. It appears on 3 Keston models in our database.
Technical description: Outside sensor failure
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 F6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston F6 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