How to Replace Your Water Heater Gas Valve

If your water is getting too hot, the pilot light isn't functioning, or the heat limiter trips, there's a good chance that your water heater gas valve isn't working properly. These are all tell-tale signs that there might be a problem and it's time to replace the gas valve.

This article will not only give you step-by-step directions on how to replace the gas valve yourself, but also help you troubleshoot to determine if it is the issue. Whether you choose to do the job yourself or call a professional plumber, you'll be armed with the information you need to know to get your water heater back to performing as it should.

How a Gas Control Valve Works

A water heater gas valve is also referred to as a gas thermostat, gas control valve, or control valve. It's located on the outside of the heater near them bottom, and it's easy to identify since it connects to the gas line. 

The gas control valve is an essential part as it manages the flow of gas to the water heater. It has three primary functions: Controlling pilot light, managing the water temperature, and it's also a high temperature safety device. Let's take a closer look at each:

Pilot Light - In order for a gas water heater to heat water, the pilot light must be lit. In order to light the pilot light, a button, which is located on the gas control valve, is pressed. When the button is pressed, enough gas is allowed to flow to ignite the pilot light.

Once lit, the pilot light's role is to heat the thermocouple until it reaches the required temperature to send a signal back to the gas control valve. Upon receiving the signal, the gas control valve engages the burner and the water within the tank begins to heat.

Water Temperature - Within the gas control valve are two probes: A temperature probe and a high limit probe. The temperature probe senses the temperature of the water and opens the gas valve when the water temperature drops below the set point. With the gas valve open, the burner is able to ignite and heat the water back to the set point temperature.

High Temperature Limit - The high limit probe also senses the temperature of the water, however, it's a safety device in case the thermostat should ever malfunction. When the high limit probe senses that the water temperature is too high, it shuts down the valve that supplies gas to heater, and thus, prevents the water heater from heating the water to an unsafe level. 

Troubleshooting Gas Control Valve Issues

If you suspect that there's a problem with the gas control valve, you'll want to do some troubleshooting. It's always possible that the problem isn't actually the control valve, but rather one of the components, such as the high limit probe, thermostat, pilot light, or even the gas burner. The issue could also be something simple like a clogged sensor or tube.

In fact, it's more likely that the thermocouple is defective, rather than the gas control valve. If this is the case, the thermocouple can be replaced relatively easily and for far less money.

Pilot Light Troubleshooting

Never attempt to light the pilot light if you smell gas. Always follow the pilot lighting instructions for your water heater.

If your pilot light frequently goes out or won't stay lit check the following:

• Press the pilot button on the gas control valve. If the pilot light ignites but will not stay lit when you release the pilot button, the problem may be with the thermocouple.
• If you replace the thermocouple and the pilot light still won't stay lit when you release the pilot button, then your problem is with the gas control valve.
• If you're unable to get the pilot light to ignite, check the gas supply line. It's possible that the valve was inadvertently turned off, or there's a kink in the hose.
• If there isn't a problem with the gas supply to the water heater and the pilot light does not ignite, it's possible that there's a clog in the pilot line or orifice. 

Working with natural gas is very dangerous, if you feel the least bit insecure with your skills, we recommend calling a professional plumber to help you troubleshoot and resolve the problem.

High Limit Probe

It's important to note that if the high limit probe was tripped, it can not be reset. The high limit probe will shut down the gas valve if the thermostat malfunctions and the water within the tank reaches an unsafe temperature.

When this happens, you'll need to replace the gas control valve. By replacing the control valve you'll have peace-of-mind that the issue was resolved.

Troubleshooting a Clogged Tube or Orifice

If your water heater isn't heating water, the burner isn't firing up, and the pilot light is on, it's possible you have a clogged tube or orifice. Here are some steps to troubleshoot this problem:

• Check the burner orifice. If it's clogged you'll need to clean it as well as the burner supply tube.
• Under the burner, at the end of the burner supply line is the burner assembly. Remove the burner assembly in order to access the orifice.
• If after cleaning the burner supply tube and the orifice, you're still having problems, then the issue is the water heater's gas control valve.

Other Gas Control Valve Issues

There are a few other issues that can cause your gas control valve to malfunction. It's important to note, that you can not repair a gas control valve. If there is a problem, you must replace it.

• If the control knob does not turn, you need to replace the valve. Never force the knob.
• If the pilot button becomes stuck and doesn't pop-up when released, your control valve will need to be replaced. Be sure to turn off the gas to play it safe.

How to Replace a Gas Control Valve

Replacing a gas control valve is a relatively simple task that can be done by the homeowner. If you do not feel comfortable, you should call a qualified plumber to do the repairs.

Safety should always be your number one priority. You should not smell gas. If you do, there may be a more serious problem. Turn the gas off to the water heater and the gas company.

Keep in mind, that there are several different types of control valves on the market, so yours may be slightly different. It's always best to follow the instructions that come with the control valve to ensure you are setting it up properly.

Step One - Turn Off the Gas

• On the front of the gas control valve is a knob to the thermostat. Turn the knob to the "off" position.
• Next, locate the valve on the incoming gas line that attaches to your water heater. You'll find a valve with a lever. The lever should be in the "on" position as indicated by being inline with the gas pipe.
• Turn the lever "off" by turning it 90-degrees or 1/4-turn so that it's perpendicular to the pipe. When the lever is in the off position it will not allow gas to flow to your water heater.

Step Two - Turn Off the Water

• Turn off the incoming water supply by locating the water inlet line that enters the top of the water heater.
• The water inlet line will either have a gate valve (dial type) or a ball valve with a lever like the gas valve.
• Close the valve by either turning the gate valve dial until it stops, or turning the lever 90-degrees.

Step Three - Drain the Tank

Now that you've turned off the gas and incoming water to the water heater it's time to drain your tank. Here's how:

• Open a hot water faucet inside your house.
• Attach a hose to the drain valve located at the bottom of your water heater and run the other end outside or to a floor drain.
• Open the drain valve and allow the heater to drain until empty. Use caution, the water will be hot.
• If it's been awhile since you have drained your water heater, you may find that the valve either drains slow or is clogged. This article will help you unclog your drain valve. 

Step Four - Disconnect the Gas Line

• Disconnect the gas supply line to the gas control valve using a wrench.
• Remove the adapter that connects the gas supply line to the gas control valve.

Step Five - Disconnect the Burner Assembly

• Remove the burner assembly cover plate from the bottom of the water heater.
• Disconnect the red and white wires from the gas control valve. Use caution when disconnecting since you'll be using them on the new control valve.
• Unplug the piezo switch.
• Disconnect the gas line that feeds into the burner assembly.
• Disconnect the thermocouple connector.
• The gas control valve should no longer be connected to the burner assembly or the incoming gas line.

Step Six - Remove the Burner Assembly

• Remove the screws that hold the burner assembly in place.
• Gently pull the burner assembly from the water heater.

Step Seven - Remove the Gas Control Valve

• Screw a 1/2-inch nipple into the gas control valve where you removed the incoming gas line adapter.
• Using the 1/2-inch nipple as a wrench, turn the gas control valve counter-clockwise until you are able to remove it from the water heater.
• Remove the 1/2-inch nipple from the "old" control valve and set the gas control valve aside.

Step Eight - Install the New Gas Control Valve

• Insert the 1/2-inch nipple into the "new" gas control valve.
• Wrap the threads on the control valve several times with teflon tape. This will prevent it from leaking.
• Carefully insert the gas control valve into the water heater. Use the 1/2-inch nipple to turn it clockwise until it is firmly in place. 
• The new gas control valve should be level and the connection points should be facing downward.
• Remove the 1/2-inch nipple.

Step Nine - Replace the Burner Assembly

• Replace the burner assembly parts with new parts if needed.
• Slide the burner assembly back into place. Be sure that it slides into the "notch" so it is securely in place.
• Connect the burner assembly gas line to the gas control valve.
• Connect the thermocouple connector to the gas control valve.
• Insert the four screws that secure the burner assembly in place.

Step Ten - Connect the Gas Control Valve

• Connect the red and white wires into their respective slots.
• Connect the piezo switch.
• Check that there is a spark by looking through the sight glass and pressing the piezo switch.
• Tighten the connections to the burner assembly gas line and the thermocouple with a wrench. They should be secure, but not too tight.
• Replace the burner assembly cover, and secure it in place.

Step Eleven - Connect the Gas Line

• Double check that the drain valve is closed on the water heater.
• Open the water inlet valve to allow the tank to fill with water.
• Line the gas adapter with both teflon tape and pipe dope.
• Insert the adapter into the gas control valve and tighten with a wrench.
• Attach the gas line to the adapter.
• Once water begins to flow through the open faucet inside your house, your water heater is full. You can close the faucet.
• Open the gas valve by turning the level so that it's inline with the gas pipe.
• Check for gas leaks on the gas line connection points using a soapy water mixture. If you see bubbles, you need to check your connection, you have a gas leak.

Step Twelve - Light the Pilot Light

• Leave the gas control valve in the "off" position with the gas line open for at least five minutes before lighting the pilot.
• Then, turn the control valve to "pilot" and press and hold the button.
• While the button is pressed, press the piezo switch multiple times.
• It may take a minute or two before the light switches on and you can turn the control valve from "pilot" to a temperature setting. 

Watch the Video

Regulating the Temperature

The gas control valve also has a dial that allows you to adjust the temperature setting. Frequently, the temperature settings are: Low; Medium; and High, which isn't much help, so it's a good idea to test the temperature at the faucet after the water heater has fully heated the water. You can find directions on how to do this HERE. 

The faucet temperature should be between 120° F. and 130° F. which is not only the most cost-effective, but also the safest setting. When your hot water is below 120° F. you run the risk of Legionnaire's disease, and above 130° F. you risk scalding injuries.