How to Test a Furnace Thermocouple with a Multimeter

Published: July 21, 2026 — BC Wide Home Services Ltd, doing business as BC Wide Heating & Air Conditioning — Greater Vancouver, BC

What You Need

To test a thermocouple: a digital multimeter with millivolt (mV) setting, the furnace access panel removed, and the pilot light burning. The test measures the voltage generated by the thermocouple when heated by the pilot flame.

Testing Procedure

Set the multimeter to DC millivolts (mV). Attach one lead to the copper thermocouple tube and the other to the thermocouple connector at the gas valve. Light the pilot and hold the reset button for 30 seconds. A good thermocouple reads 25-35 mV. Below 15 mV indicates a weak thermocouple needing replacement.

Replacement Cost

Thermocouple replacement costs $20-50 for the part. Professional installation with service call: $150-250. DIY replacement is straightforward — the thermocouple screws into the gas valve and clips into a bracket near the pilot.

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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.