Burner lights briefly then goes out, repeated attempts then A02 lockout on display

Safety warning: Switch off power and close the gas valve before opening the combustion chamber. Risk of gas leak and burns.

Steps:

• Check flue and air intake: Ensure the concentric flue terminal is not blocked by leaves, snow, or debris. A blocked flue can cause unstable combustion and flame loss.
• Inspect ionisation electrode: Remove the burner cover. Locate the flame sensor (ionisation electrode). Clean it with fine abrasive paper and ensure the tip is in the flame area as per the service manual. Check the cable for damage and secure connection to the control board.
• Clean burner head: On De Dietrich condensing boilers, the premix burner surface can clog with dust or combustion residues. Gently brush the burner mesh or perforated plate with a soft brush and vacuum loose debris. Do not deform the burner surface.
• Check gas supply stability: If other gas appliances flicker or go out, contact your gas supplier to check pressure. Do not attempt to adjust the gas valve.
• Reset and test: Restore gas and power, reset the boiler, and observe. If the flame still extinguishes after a few seconds, further combustion analysis with a flue gas analyser is required.

Professional help: A technician should verify gas valve modulation, combustion quality, and replace the ionisation electrode or gas valve if necessary.