Boiler will not start; display shows E01 shortly after a heat or hot water demand.

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 / licensed gas technician should work on gas-carrying components and combustion settings.

• Check gas supply: Verify that the gas isolation valve to the CTC boiler is fully open. Confirm other gas appliances in the property work. If not, contact your gas supplier.
• Reset the boiler: Restore power, then press and hold the reset button on the CTC control panel (or follow the reset procedure in the CTC user manual). Observe if E01 reappears.
• Inspect flue and air intake: Ensure the concentric flue terminal is not blocked by debris, snow, or nests. A blocked flue can prevent proper ignition.
• Check ignition components (technician): Remove the front casing, then the combustion chamber cover. Inspect the ignition electrode and ionisation electrode for cracks, heavy soot, or incorrect gap. Clean with fine emery cloth and refit, or replace the electrode set if damaged.
• Check burner (technician): Remove and inspect the premix burner for heavy contamination or damage. Clean or replace the burner insert as specified by CTC.
• Gas valve and pressure (technician): Measure inlet and burner pressure at the CTC gas valve test points. If pressures are incorrect, adjust only according to the CTC service manual or replace the gas valve assembly.