How to Test a Furnace Pressure Switch with a Multimeter

Published: July 23, 2026 — BC Wide Home Services Ltd, doing business as BC Wide Heating & Air Conditioning — Greater Vancouver, BC

What You Need

A digital multimeter (set to continuity or ohms), screwdriver to remove the furnace panel, and access to the pressure switch (near the inducer motor). The furnace must be off and cool before testing. Always turn off power at the breaker.

Testing Procedure

Disconnect the two wires from the pressure switch terminals. Set the multimeter to continuity (or ohms). Touch the probes to the two terminals. With the furnace OFF and the inducer not running, the switch should be OPEN (no continuity, reading OL). Start the furnace — when the inducer runs, the switch should CLOSE (continuity, near 0 ohms).

Interpreting Results

If the switch does not close when the inducer runs: the switch may be faulty, or the inducer may not be creating enough draft (blocked vent, bad inducer). If the switch tests OK but the furnace still has a pressure switch error, the issue may be the wiring, control board, or venting — call for professional diagnosis.

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Safety Reminder

If you smell gas, suspect carbon monoxide or believe there is an immediate danger, leave the property and contact emergency services or the appropriate gas emergency authority. Do not remain inside — exit the building immediately and call for help from outside.