Unit locks out with A03, fan may start briefly then stop, no ignition attempt is heard.

Safety: Turn off power and gas. Allow the unit to cool completely before touching internal components.

• 1. Check for obvious blockages: Inspect the external flue terminal for obstructions (ice, leaves, bird nests). Ensure the air intake and exhaust are clear.
• 2. Reset high-limit thermostat (if manual reset type): On some Ferroli models, a manual reset flue or overheat thermostat is mounted on the heat exchanger. Press the small reset button if present. If it trips again, do not keep resetting—find the cause.
• 3. Verify water circulation (for models with pump): Ensure system valves are open and that the circulation pump runs when there is demand. Airlocks or closed valves can cause overheating.
• 4. Clean heat exchanger: A scaled or sooted heat exchanger can overheat. A technician should remove and chemically descale or brush-clean the Ferroli heat exchanger as per the service manual.
• 5. Replace faulty thermostat: If the flue/overheat thermostat is open-circuit at normal temperature, it must be replaced with the correct Ferroli spare.

Persistent A03 faults require a professional flue and combustion check to ensure safe operation.