Exhaust and air intake pipe check during startup

What is going on

Use this when the furnace shuts off at the pressure switch, or when a flame rollout switch opens. Both often trace back to the venting. Before opening any panel or resetting anything, turn off power at the disconnect and make sure the furnace has cooled. An open rollout switch means flame came out of the burner box at some point, which is a real safety event, so find the cause before you put the furnace back in service.

Likely causes

• Obstructed exhaust pipe
• Loose exhaust or intake connection
• Blocked termination from snow, ice, leaves or a nest
• Opened flame rollout switch caused by obstructed pipe
• Cracked or leaking pipe section

Check in this order

1. Turn off power and let the furnace cool before opening any panel.
2. Check exhaust and air intake connections for tightness.
3. Check the pipe for blockage along its full length.
4. Confirm the pressure switch is closed when the inducer runs; an obstructed exhaust makes the unit shut off at the switch. Use a meter across the switch to confirm.
5. Check the termination for blockages.
6. Reset the manual flame rollout switches on the burner box only after the cause is found and corrected. Do not defeat any safety.
7. If rollout trips again, call a licensed technician.

More furnace guides

• Annual planned service inspection
• Annual service checklist
• Blower access panel and carbon monoxide hazard
• Burner assembly cleaning
• Change blower speed tap
• Check temperature rise and adjust blower speed