Furnace shows A04, burner does not start, fan may run briefly, flue fan may not start

Safety: Turn off power and gas. A flue fault can lead to dangerous combustion gases indoors. Do not operate the furnace until the cause is identified.

• Check flue terminal: From outside, inspect the Beretta flue terminal for ice, leaves, bird nests, or other obstructions. Clear any blockage carefully.
• Inspect flue pipe: Visually check accessible sections of the flue for disconnections, crushing, or signs of condensation leakage. Do not dismantle sealed flue joints unless you are qualified.
• Check flue thermostat: Locate the flue safety thermostat on the flue hood or near the combustion chamber. Ensure its wiring is intact and connectors are tight. Some models have a manual reset button—press only after the unit has cooled and the flue is confirmed clear.
• Verify flue fan operation: On start-up, listen for the flue fan (exhaust fan) to run. If it does not start, or is noisy and slow, the fan or its capacitor may be failing and should be replaced by a technician.

If A04 reappears after clearing obvious obstructions, contact a qualified Beretta service technician for flue gas analysis and safety checks.