Safety first: Turn off power and gas before working on venting or the inducer assembly. Combustion gases are hazardous.

Check vent terminations: Go outside and inspect the furnace exhaust and intake pipes. Remove snow, ice, leaves, or nests. Ensure vent screens are clear.
Inspect tubing: Inside the furnace, remove the rubber tubing from the pressure switch and inducer port. Check for water, kinks, or splits. Clear any moisture and reattach firmly.
Test inducer motor: Restore power and call for heat. Confirm the inducer starts promptly and runs smoothly. Listen for grinding or humming. If the inducer does not start or is noisy, it may need replacement.
Check switch operation: With a multimeter, verify the pressure switch closes (shows continuity) only when the inducer is running. If it never closes despite good inducer and clear venting, replace the pressure switch.

Do not attempt to adjust or bypass the pressure switch; it is a critical safety device.

Status LED flashes 3 times; furnace starts but shuts down before or shortly after ignition

Possible Causes