Low stage pressure switch open, induced draft blower runs continuously

What is going on

Induced draft blower keeps running and the furnace does not continue to operate.

Likely causes

• Pressure switch hose blocked, pinched or connected improperly
• Blocked flue and/or inlet air pipe, blocked drain system, or weak induced draft blower
• Incorrect pressure switch set point or failing switch contacts
• Loose or improperly connected wiring

Check in this order

1. Inspect the pressure switch hose and repair or replace it if needed.
2. Inspect flue and/or inlet air piping for blockage, correct length, elbows and termination. Check the drain system.
3. Check induced draft blower performance and correct as needed.
4. Correct the pressure switch set point or contact action.
5. Tighten or correct the wiring connection.
6. Turn power off before repair.
7. Replace the pressure switch or the induced draft blower with the correct part if they fail.

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)