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How To Check And Replace A Gas Control Valve On A Furnace

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The summer is a good time to inspect your gas furnace and get it ready for the coming fall and winter.  You should turn on the furnace and make sure it runs well. If the furnace doesn't produce heat, you need to start checking the parts in the furnace to make sure they are functioning properly. One part you should check is the gas control valve. If the valve is faulty, gas won't be able to pass through the external gas line to the burner in the furnace. Here is how you can check a gas control valve and replace it if necessary.

You Will Need:

  • Voltmeter
  • New Gas Control Valve

Testing the Valve

You can check your gas valve using a voltmeter. Attach the prongs of the voltmeter (one is red and the other is black) to the electrical terminals on the gas valve. Connect the red prong to the terminal that has the red wire attached to it, and connect the black prong to the terminal with a white wire running to it.

You should get a reading on your voltmeter that matches the volts required to operate the gas control valve (this information is usually stamped into the valve). Your voltmeter reading should match the amounts of volts needed to open and shut the gas valve. If the gas valve has 24 volts stamped on it, the voltmeter should show 24 volts on the monitor screen. If the reading doesn't match the requirements of the valve, you'll need to replace it.

Replacing Gas Valve

Remove the old gas control valve by doing the following:

  1. Shut the furnace down and turn off the gas and electrical power going to the furnace.
  2. Disconnect the two wires going to the gas control valve by detaching them from the electric terminals.
  3. Disconnect the gas line going to the control valve.
  4. Remove the harness the gas control valve and the internal gas line are connected to, and then pull them away from the furnace so you have room to unscrew the entire valve mechanism from the internal gas line.

You should take the gas control valve with you to the hardware or furnace supply store to make sure you get the correct replacement valve.

Put Teflon tape on the threads of the internal gas line and screw the valve onto it. Screw the internal gas line and valve back onto the harness. Reconnect the external gas line to the control valve (use Teflon tape on the threads of the valve). Reconnect the wires to the valve and turn the gas on.

You want to check for gas leaks at the connection points. If there aren't any leaks, restore the electricity and turn the furnace back on. You'll know you are done once you feel hot air coming out of the heating vents. If you don't have success or don't feel comfortable attempting this yourself, contact a local furnace repair company.