BoilerFaultCodesKeston L1 Fault Code
The Keston L1 fault code means: your boiler has shut down because the water inside the unit has become too hot, likely due to a circulation problem.. It appears on 5 Keston models in our database.
Technical description: Flow temperature overheat
DIY fix possible
Check that your radiator valves are open to allow water to flow through the system.Ensure your system pressure is between 1 and 1.5 bar on the pressure gauge.Reset the boiler by turning the control knob to the 'Reset' position for five seconds.
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Keston models that show the L1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston L1 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