BoilerFaultCodesKeston E18 Fault Code
The Keston E18 fault code means: your boiler has detected that the water inside is getting too hot because it is not moving around your heating system quickly enough.. It appears on 7 Keston models in our database.
Technical description: Flow overheat – check water circulation
DIY fix possible
Check that at least two or three radiator valves are fully open to allow water flow.Ensure your external heating pump (if visible) is running and not making a loud humming noise.Check your boiler pressure gauge and top it up to 1.5 bar if it is too low.
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Gas Safe Register →Keston models that show the E18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston E18 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