BoilerFaultCodesKeston F2 Fault Code
The Keston F2 fault code means: your boiler has lost its flame signal during operation, meaning and it can no longer safely heat your water or radiators.. It appears on 8 Keston models in our database.
Technical description: Flame loss
What causes the Keston F2 fault?
This fault occurs when the boiler's internal sensor can no longer detect a steady flame while the system is running. The most common reasons include a buildup of carbon on the sensing probe, a failing gas valve that isn't providing enough fuel, or an unstable electrical signal that causes the safety system to shut the boiler down.
This fault is more common in extremely cold weather, as freezing temperatures can affect the external flue pipes and cause consistent flame instability.
DIY fix possible
Check that your gas emergency control valve is in the 'on' position and you have credit on your gas meter.Inspect the outdoor condensate pipe for signs of freezing or blockages if the weather is very cold.Press the Reset button for two seconds to see if the system reignites.
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Gas Safe Register →Keston models that show the F2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston F2 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