Safety: Turn off power and lock out the breaker. Ensure gas is off before opening panels.

Inspect intake and exhaust: Check the IVT concentric flue or twin-pipe system outside the building. Remove any ice, leaves, nests, or debris blocking the intake or exhaust terminals.
Check combustion fan wheel: Remove the burner/combustion chamber cover to access the combustion fan assembly. Spin the fan wheel by hand; it should rotate freely without scraping. Clean dust buildup with a soft brush and vacuum.
Verify wiring: Inspect the plug from the combustion fan motor to the IVT control board. Reseat the connector and look for burnt pins or damaged wires.
Restart and listen: Restore power and call for heat. If the fan hums but does not start, the motor is likely seized or the capacitor (if external) is faulty and the fan assembly should be replaced.

Do not operate the furnace with a known flue blockage or defective combustion fan. This can cause dangerous flue gas spillage.

Furnace attempts to start but shuts down during pre-ignition; combustion fan runs briefly then stops

Possible Causes