Boiler locks out with flue/combustion fault, may start then shut down repeatedly

Safety: Combustion and flue work must be carried out by a qualified heating engineer with flue gas analysis equipment. Do not alter burner settings yourself.

• Visual flue check: Ensure the flue is intact, properly supported, and not damaged. Check for signs of corrosion or disconnection.
• Check for obstructions: Confirm that no objects have been placed over or near the flue terminal that could restrict exhaust gases.
• Reset and observe: Reset the boiler and observe operation. If the boiler repeatedly starts and stops with A06, stop resetting and arrange professional service.
• Professional service: A technician should clean the primary heat exchanger, check burner head and baffles, verify combustion with an analyser, and adjust the Riello burner (air shutter, gas valve or oil pump pressure) to manufacturer specifications.