Boiler will not ignite, display shows E01 and burner does not light

Safety first: Turn off electrical power to the boiler and isolate the gas supply before removing any covers. Only a Gas Safe registered engineer should work on gas-carrying components.

Basic user checks:

• Verify that the gas supply to the property is on and other gas appliances work.
• Check system pressure on the Keston boiler gauge (typically 1.0–1.5 bar when cold). Top up via the filling loop if below 1.0 bar.
• Reset the boiler using the front panel reset button as per the Keston user manual. Observe if E01 reappears.

Technical checks (engineer only):

• Remove the combustion chamber cover and inspect the ignition electrode and flame sensor on the Keston burner assembly for cracks, carbon build-up, or damage. Clean gently with fine emery cloth or replace as a set if worn.
• Check the ignition lead from the PCB to the electrode for signs of arcing, burns, or loose connections. Reseat or replace the lead if insulation is damaged.
• Using a manometer, confirm correct gas inlet pressure and that the Keston gas valve is being energised during ignition (check 230 V or control voltage at the valve coil as per wiring diagram).
• Verify correct polarity and earth at the boiler supply; incorrect polarity can prevent flame detection.
• If ignition spark is present but no flame is established, test and, if necessary, replace the gas valve assembly with the correct Keston part.