How to Troubleshoot Thermocouples

Gas appliances that have a pilot light also have a thermocouple. The thermocouple senses the heat of the pilot light and maintains the flow of gas. If the thermocouple senses no heat from the pilot light, meaning it has been extinguished, the thermocouple shuts off the flow of gas. The thermocouple acts as a safety feature to prevent unburnt gas from filling the home. You can troubleshoot a thermocouple with a common electrical device and by following the right procedure.

Things You'll Need

• Set of screwdrivers
• Multimeter

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Instructions

1. Shut off power to the appliance by unplugging the electrical cord or turning off the circuit breaker. Even though the appliance is gas, it may have an ignitor that uses electricity. Shut off the gas supply to the appliance by locating the closest shutoff valve on the gas line and twist it completely clockwise.

2. Plug in the testing probes on the ports of a multimeter labeled for testing resistance and not volts. Turn the ohm selector knob to the lowest setting available.

3. Remove the pilot light access panel with a screwdriver. The panel is typically located where the gas line enters the appliance. One end of the thermocouple is connected to the pilot light, and the other is connected to the gas line.

4. Touch one probe of the multimeter to each of the thermocouple terminals. The multimeter should register zero or close to a zero reading. If the reading is much higher, the thermocouple is malfunctioning and should be replaced.

5. Transfer the probes to the multimeter ports labeled for voltage. Turn the dial to the lowest voltage setting. Touch one probe to each of the thermocouple terminals and touch the end of the thermocouple connected to the pilot light with your hand. If the thermocouple is working properly, it will register a low voltage reading on the multimeter from your hand's heat. If it does not, the thermocouple may need to be replaced.