Boiler locks out with EA on display, no flame established, burner does not ignite.

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

• Reset the boiler: Press the reset button once and observe whether the boiler attempts ignition. If EA reappears, do not keep resetting.
• Check gas supply: Ensure other gas appliances in the property work. If not, contact your gas supplier. Verify the boiler's gas isolation valve is fully open.
• Inspect the flue terminal: From outside, check that the Worcester Bosch concentric flue terminal is not blocked by debris, snow, or vegetation, which can affect combustion.
• Check condensate pipe: In freezing weather, ensure the condensate pipe is not frozen or blocked, as this can cause ignition issues. Thaw gently with warm (not boiling) water if frozen.
• Electrode inspection (engineer level): Remove the combustion chamber cover, inspect the ignition and ionisation electrodes for cracks, carbon build-up, or damage. Clean with fine emery paper and check the gap against the Worcester Bosch service manual. Replace if worn.
• Gas valve and pressure (engineer level): Using a manometer, check inlet and burner pressure at the gas valve. If pressures are incorrect or the valve is not opening, the gas valve or control PCB may be faulty and must be replaced and commissioned by a qualified engineer.