Burner locks out with pre-ventilation but no flame attempt, control indicates safety lockout before ignition

Safety: Disconnect power and ensure there is no call for heat. Do not bypass safety devices.

Steps:

• Check air intake and flue: Inspect the combustion air intake and flue pipe for obstructions (ice, nests, debris). Clear any blockage and ensure proper termination.
• Inspect air pressure switch: Locate the air/fan pressure switch on the Riello burner or furnace. Check tubing for cracks, kinks, or water. Replace damaged tubing and ensure both ports are clear.
• Test switch operation: With a multimeter, verify that the pressure switch closes when the fan runs (requires calling for heat and observing continuity). If it does not close, the switch or fan may be faulty.
• Check wiring harness: Inspect the wiring between the pressure switch, limit switches, and the Riello control box for loose or burned connectors.

If A03 remains after clearing airflow issues and verifying the pressure switch, the burner control box may need replacement and should be evaluated by a qualified technician.