Burner locks out during pre-purge, fan runs briefly then stops

Safety: Switch off power and ensure the burner cannot start automatically. Allow hot surfaces to cool.

Steps:

• Check air intake and flue: Inspect the combustion air intake and flue gas outlet for obstructions (ice, leaves, bird nests, debris). Clear any blockage. Ensure terminal guards are not clogged.
• Inspect fan: Remove the burner cover and visually inspect the combustion air fan wheel on the Weishaupt burner. Spin the wheel by hand (power off) to confirm it rotates freely and is not rubbing the housing.
• Air pressure switch: Locate the air pressure switch connected to the fan housing via silicone tubing. Check tubing for cracks, kinks, or water. Replace damaged tubing and ensure tight connections.
• Electrical checks: Confirm that the fan motor connector is fully seated on the control module and that no wires are loose or burned.
• Test run: Restore power and call for heat. Observe whether the fan starts and the pressure switch closes (you may hear a click). If the fan does not run or the switch does not prove, professional diagnosis of the fan motor and pressure switch is required.