BoilerFaultCodesKeston Flow Temperature Overheat Lockout Fault Code
Also written as FLOWTEMPERATUREOVERHEATLOCKOUT — same fault.
The Keston Flow Temperature Overheat Lockout fault code means: your boiler has switched itself off to prevent damage because the internal water temperature has become too hot.. It appears on 1 Keston model in our database.
Technical description: Overheat lockout. 1 Fill system to 1.0 bar. 2 Bleed radiators. 3 Check radiator valves open. 4 Reset boiler. 5 Contact installer.
DIY fix possible
Check the pressure gauge and top up to 1.0 bar if it is lowEnsure all radiator valves are fully openBleed any air out of the radiators and reset the boiler
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Keston models that show the Flow Temperature Overheat Lockout fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston Flow Temperature Overheat Lockout 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