Unit locks out with A03, fan may run briefly then stop, burner does not light.

Safety: Turn OFF the heater and disconnect power. Risk of carbon monoxide – do not operate the unit until the flue path is verified safe.

• Check flue terminal: Go outside and inspect the Fondital flue terminal. Remove any visible obstructions such as leaves, nests, snow, or plastic bags.
• Verify air intake (for concentric flues): Ensure the air intake annulus is not blocked by debris or building materials.
• Inspect flue sensor/thermostat: Inside the unit, locate the flue gas thermostat or NTC sensor on the flue hood or heat exchanger outlet. Check for loose wiring and signs of overheating. A tripped manual-reset thermostat (if fitted) should be reset only after the cause of overheating is removed.
• Fan operation: On fan‑assisted Fondital models, start the unit and listen for the fan. If it does not start or is noisy, the fan or its capacitor may be faulty and should be replaced by a technician.
• Chimney and draft: For chimney‑connected models, have a qualified chimney professional check draft and clean the flue system.