BoilerFaultCodesKeston E03 Fault Code
The Keston E03 fault code means: your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.. It appears on 9 Keston models in our database.
Technical description: Boiler overheat – check that any valves to the heating circuit have not been shut down, no air in the system and that the water pressure is correct
What causes the Keston E03 fault?
This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety sensor to cut the power. The most common reasons are a lack of water flow caused by a failed pump, a blockage in the pipework, or air trapped within the system preventing heat from being moved away from the burner.
This issue often appears when the heating is first turned on after summer, as internal pump components can seize up during long periods of inactivity.
DIY fix possible
Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge.Ensure all radiator valves and internal isolation valves are fully open.Bleed your radiators to remove any trapped air pockets from the system.
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Gas Safe Register →Keston models that show the E03 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston E03 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