BoilerFaultCodesKeston F1 Fault Code
The Keston F1 fault code means: your boiler has detected that the water pressure in the system is too low, causing it to stop running for safety.. It appears on 8 Keston models in our database.
Technical description: Low water pressure
What causes the Keston F1 fault?
This fault occurs when the water levels inside your heating system drop below the minimum required for the boiler to operate safely. The most common reasons for this are a leak somewhere in the pipework or radiators, or simply that air was recently bled from the system without topping the pressure back up.
This issue is frequently seen in autumn when homeowners turn their heating back on for the first time and discover the pressure has naturally dropped over the summer months.
DIY fix possible
Locate the filling loop, which is usually a flexible silver hose under the boiler.Slowly open the small tap (or taps) on the filling loop until you hear water moving.Watch the pressure gauge and close the taps exactly when the needle reaches 1.5 bar.
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Gas Safe Register →Keston models that show the F1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston F1 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