Display shows A04 and burner does not start; fan may run briefly

Critical safety warning: A flue fault can lead to carbon monoxide hazards. If you suspect flue blockage or smell exhaust, switch off the heater, ventilate the area, and contact a qualified technician immediately.

• 1. Reset once only: After the unit cools, reset it. If A04 reappears, do not continue to reset; there is a genuine safety issue.
• 2. Visual flue inspection (user level): From outside, check that the Beretta flue terminal is not blocked by leaves, snow, nests, or debris. Ensure the terminal clearances are as per the installation manual.
• 3. Check for recirculation: Make sure no other exhaust outlets or architectural features are directing fumes back into the flue terminal.
• 4. Inspect flue gas thermostat (technician): A professional should access the flue gas thermostat on the combustion chamber, test continuity, and verify correct mounting and contact with the flue path.
• 5. Verify flue installation: A Beretta-trained installer should confirm correct flue length, slope, and joint sealing. Incorrect flue configuration can cause overheating and lockouts.