Boiler locks out shortly after a heat demand, red lockout light on burner control, no flame established

Safety first: Isolate electrical power to the boiler and close the gas/oil isolation valve before removing covers. Allow the appliance to cool. If you smell gas, do not attempt repair—ventilate the area and contact a qualified technician immediately.

• Reset the burner: Press the red reset button on the Riello burner control box once. If the burner lights and runs normally, monitor for recurrence. Do not repeatedly reset a locking-out burner.
• Check fuel supply: Ensure the gas isolation valve is fully open (for gas boilers) or that the oil tank has fuel and the oil isolation valve is open (for Riello oil burners). Check for kinked or crushed flexible hoses on oil lines.
• Inspect ignition electrode: Remove the burner cover. Locate the ignition electrode assembly on the Riello burner head. Check for cracked ceramic, carbon build-up, or damaged leads. Clean the electrode tip gently with fine emery cloth and re-check the electrode gap and position according to the Riello burner manual.
• Check flame sensor (ionisation electrode): Clean the ionisation probe with fine abrasive pad. Ensure the probe is correctly positioned in the flame path and the cable is firmly connected to the control box.
• Air in oil line (oil models): If recently serviced or tank run low, bleed the oil pump via the bleed screw while running the burner in test mode (qualified personnel only) until a solid stream of oil is present.
• Call a professional: If A01 persists after basic checks, a qualified heating engineer should test ignition transformer, burner control box, gas valve or oil pump pressure, and combustion settings with proper instruments.