How to Test Furnace Control Valves

A bad gas furnace valve will prevent your entire furnace from operating. If a gas valve doesn’t open, then the furnace simply shuts down. Once your thermostat calls for heat, 24 volts of electricity flow to the valve. Because the valve requires electricity, it’s tested with a multimeter, which can measure AC voltage. The multimeter will indicate if the gas valve is bad or if the problem stems from another part in your furnace.

Multimeter

Instructions

- 1
  Turn off power to your gas furnace and remove the front panel to your furnace.
- 2
  Locate the gas furnace valve. The valve will typically have two wires connecting into it. If you’re unsure of what your valve looks like, consult your furnace's manual for a diagram. Remove the wires from the valve.
- 3
  Turn on your multimeter and set it to AC voltage. Make sure the voltage range is higher than 24. Take the black probe and connect it into either one of the valve terminals or onto the end of one of the wires that connects into the terminal. Connect the red probe to the opposite wire or terminal.
- 4
  Set your thermostat to a high temperature, so that it will call for heat. Power on your furnace.
- 5
  Look at your multimeter. It should read “24” volts or more at some point. If it reads 24 volts and then immediately drops down, it’s likely that your valve is bad. If it never reads 24 volts, then something is likely preventing power to the valve in the first place, which is usually indicative of another problem. You’ll have to test other parts in your furnace to determine what that problem is.

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