How to Test & Replace Your Thermocouple to Your Water Heater/Furnace

Meter Test Under Load

• 1

  Turn off the gas supply to the water heater or furnace. Turn the gas petcock 90-degrees clockwise to shut off the gas supply.

• 2

  Set a digital multimeter to the millivolt range. Connect the positive lead to the thermocouple terminal on the gas valve.

• 3

  Connect the negative lead to the metal thermocouple tubing.

• 4

  Heat the end of the thermocouple tube with a grill lighter. Make sure to cover the entire end of the tube with the flame.

• 5

  Heat the tube for 30 seconds and check the reading on the multimeter. Replace any thermocouple that registers less than 9 millivolts.

Meter Test Without Load

• 6

  Turn off the gas supply by turning the gas cock 90 degrees clockwise.

• 7

  Unscrew the thermocouple from the gas valve by turning it counterclockwise with an adjustable wrench.

• 8

  Connect the positive lead of a digital multimeter to the center conductor of the thermocouple. Connect the negative lead to the thermocouple tubing.

• 9

  Heat the end of the thermocouple with a grill lighter for 30 seconds.

• 10

  Check the reading on the multimeter. Replace any thermocouple that registers less than 20 millivolts.

Replacement

• 11

  Close the gas petcock to shut off gas to the water heater or furnace.

• 12

  Disconnect the pilot light supply tube, the gas tube and the thermocouple from the gas valve with an adjustable wrench.

• 13

  Remove any screws or bolts holding the burner to the frame of the water heater or furnace.

• 14

  Slide the burner assembly out of the furnace or water heater to expose the thermocouple.

• 15

  Pull the thermocouple out of the retaining clips or unscrew it from the burner assembly and discard it.

• 16

  Insert a new thermocouple in the burner assembly. Place the burner assembly in the furnace or water heater. Install any retaining screws or bolts and tighten them.

• 17

  Connect the gas tubes. Route the thermocouple tube to the gas valve and connect it. Tighten all connections securely.

• 18

  Turn the gas petcock 90 degrees counterclockwise to start the flow of gas. Light the pilot light and set the furnace or water heater according to the manufacturer's instructions.