BoilerFaultCodesKeston E40 Fault Code
The Keston E40 fault code means: your boiler has switched off because there is too much water pressure in the system, which can put unnecessary strain on the internal seals.. It appears on 9 Keston models in our database.
Technical description: Water pressure too high - You have put too much water pressure in your system
What causes the Keston E40 fault?
This fault occurs when the water pressure inside your heating system exceeds safe operating limits. The most common reason is that the filling loop valve has been left slightly open or is leaking, allowing too much water to enter the system from the mains. Over time, this extra water pushes the pressure high enough that the boiler shuts down to protect its internal components.
DIY fix possible
Check that the filling loop valves are fully closedSwitch off the boiler and allow it to coolBleed water from a radiator using a bleed key into a containerMonitor the pressure gauge until it returns to between 1.0 and 1.5 bar
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Gas Safe Register →Keston models that show the E40 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston E40 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