How to Troubleshoot a Thermocouple With an Ohmmeter

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Thermocouples are a type of transducer, which means they convert one form of energy (heat) into another (electrical signal). They can be found in various forms on equipment where heat must be regulated, like furnaces or clothes dryers. An ohmmeter can perform one vital test on a suspect thermocouple, while a multitester can perform two. Use a multitester, which measures both voltage and resistance, if one is available.

Things You'll Need

  • Ohmmeter or multitester (also called a multimeter)
  • Turn off the power to the equipment you are checking. If a pilot light is present, turn that off as well.

  • Rotate the dial on the multitester to the lowest ohm reading available. Make sure the tester is set to measure resistance, not voltage. Usually, this is done by placing the wire leads into the correct ports on the tester, which are labeled. This first test will determine if there is a short inside the thermocouple.

  • Touch one probe to either terminal of the thermocouple. A functioning thermocouple should give a very low to zero ohm reading. If it reads higher, the thermocouple is not working correctly and will need to be replaced.

  • Rotate the multitester dial to the lowest voltage setting possible and switch the wire leads to the ports to read voltage.

  • Place one probe on either thermocouple terminal. Touch the end of the thermocouple. Your hand should give off just enough heat for the thermocouple to create a very low voltage reading on the multitester. If no voltage is observed, the thermocouple is bad and needs to be replaced.

Tips & Warnings

  • Even though working with thermocouples means working with extremely low voltages that are not harmful, other components around the device may have exposed wiring or terminals that can cause an electrical shock. It is always wise to turn off power to equipment before testing or servicing.

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