Boiler locks out, burner does not ignite, red fault LED on, display shows A01

Safety first: Turn off the boiler at the main switch and close the gas isolation valve before removing any covers. Allow the appliance to cool fully. If you smell gas, ventilate the room and contact a gas-safe technician immediately.

Step-by-step checks:

• Reset the boiler: Press the reset button as described in the De Dietrich user manual. If A01 returns repeatedly, continue with the checks below.
• Check gas supply: Ensure the gas isolation valve to the boiler is open and other gas appliances in the property work. If no gas, contact your gas supplier.
• Inspect burner area (qualified person only): Remove the front casing and combustion chamber cover. Check the burner for heavy soot, rust flakes or debris. Clean gently with a soft brush and vacuum (do not damage the burner mesh).
• Check ignition electrode: Look for cracked ceramic, damaged cable, or heavy carbon deposits. Clean the tip with fine emery cloth. Ensure the electrode gap and position match the De Dietrich service manual. Replace the ignition electrode assembly if damaged.
• Check ionisation (flame) electrode: Clean the rod, check insulation and cable. Ensure it is correctly positioned in the flame. Replace if cracked or corroded.
• Gas valve operation (technician only): Verify that the gas valve receives power during ignition and that inlet gas pressure is within specification. Adjust or replace the gas valve if faulty.

When to stop: If you are not gas-certified, limit yourself to visual checks and resets. Any work on the gas train, combustion chamber, or flue must be done by a qualified heating engineer.