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

Safety first: Turn off the boiler at the main switch and close the gas isolation valve before removing any covers. Only a qualified gas technician should work on gas-carrying components.

• Check gas supply: Verify that the external gas cock to the Hoval boiler is fully open. Confirm other gas appliances in the property work. If there is no gas, contact your gas supplier.
• Reset the boiler: After confirming gas supply, press the reset button as described in the Hoval user manual. If A01 reappears repeatedly, do not continue resetting.
• Inspect ignition electrode: With power and gas off, remove the burner access panel. Check the ignition electrode for cracks, heavy oxidation, or damage. Ensure the electrode gap and position match the Hoval service manual. Clean light deposits with fine emery cloth.
• Check flame sensor (ionisation electrode): Clean the electrode tip with a non-abrasive pad. Ensure the cable connection is tight and not heat-damaged.
• Gas valve and wiring: Visually inspect the gas valve harness and connectors on the control board for loose or burnt pins. Do not adjust gas valve settings yourself; if wiring is intact and the fault persists, call a certified Hoval service technician.