BoilerFaultCodesKeston F3 Fault Code
The Keston F3 fault code means: your boiler has detected an issue with its fan, meaning it cannot safely circulate air or clear exhaust fumes and has shut down as a safety precaution.. It appears on 8 Keston models in our database.
Technical description: Fan fault
What causes the Keston F3 fault?
This fault occurs when the boiler's internal computer is unable to communicate with or control the fan, which is essential for pushing harmful exhaust gases out of the flue. The most common reason is that the fan motor has physically burnt out or stopped spinning, though it can also be triggered by loose electrical connections or a fault on the main control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Keston models that show the F3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston F3 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