How to Replace a Water Heater Control

Do you think your gas water heater control is faulty? Here’s how to replace it.

Is your water heater not working as effectively as it could? Maybe your water is getting too hot, the pilot light isn’t working or the heat limiter has tripped. It could be time to replace your water heater control valve.

Also called a gas valve, this unit is located on the exterior of your water heater near the bottom of the tank. Replacing it is something you can do yourself. Let’s look at what the water heater control does, what can go wrong and how to replace it.

What Is a Water Heater Gas Control Valve?

In simple terms, the water heater gas valve controls the flow of gas, which burns to heat your water.

When you press the button on your pilot to light it, a small amount of gas is released to the pilot head. Once lit, it heats the thermocouple (a temperature sensor). This, in turn, sends an electrical current to the gas control valve (1).

When the gas valve receives the electrical current, an electromagnet opens a safety valve to let gas flow to your pilot. This is what keeps it alight.

At the back of the water heater gas valve, there are two probes. One is a safety device that interrupts the gas flow if your thermostat malfunctions. The other is a temperature probe which has a lever to turn the gas on and off depending on the setting of the thermostat.

Identifying a Faulty Water Heater Control

There might be a fault with your water heater control valve if:

  • Your pilot light won’t stay alight. It could be an issue with the thermocouple. However, if you have changed this and it still won’t stay alight, your gas valve could be at fault.
  • Your water heater burners are still running with the thermostat turned right down. The gas valve could be the culprit. You might notice this if your water is too hot.
  • Your thermostat is turned up full and your burner isn’t firing. It could a faulty water heater control. This would be indicated by a lit pilot but a tank full of cold water.
  • Your pilot control won’t pop back out when you press it. You need to change the gas valve control.
  • The control knob on your water heater is stuck. Forcing it could cause damage. Replace your water heater gas valve instead.

Other things could be causing your water heater to malfunction. You might want to check for these as well. They include:

  • Poor water flow into the heater, reducing the volume, causing it to overheat.
  • A build-up of dirt or debris in the heating chamber is leading to poor temperature regulation.
  • A faulty thermostat or thermocouple.

You can replace the thermostat, thermocouple, or the safety heat limiter. However, it’s only a little more expensive to replace the whole heater control unit.

How to Replace a Water Heater Control

Now you know what your gas valve control does and how to recognize when it might be faulty. So, it’s time to learn how to change it.

1. Turn Off The Gas Supply

Whenever you are repairing or replacing anything fueled by gas, you must turn the gas supply off. To do this:

  1. Locate the thermostat on the front of the gas valve and turn the dial to off.
  2. Follow the gas supply pipe from the water heater control until you find a lever.
  3. The lever is parallel with the pipe when it’s on.
  4. Turn the lever so it’s at a 90-degree angle to the pipe.
  5. This turns your gas supply off to your water heater.

Bear in mind, if you smell gas at any time while doing this, call the gas supply company. There could be a problem they need to rectify for you.

2. Turning Off the Water Supply

Once the gas to your water heater is off, you need to turn off the water supply. The valve that does this is usually found on the inlet pipe for cold water. This will be located near the top of the water heater.

There are two types of valves. One is a gate valve and the other a ball valve.

The ball valve has a lever similar to that on the gas pipe. Turn this 90 degrees to stop the cold water supply.

The gate valve has a knob or handle that turns. Close this until it stops.

3. Drain your Water Heater

The next step is to drain the tank of water.

  1. Open the hot water faucet in a sink or tub in the home.
  2. Locate the drain valve at the base of your water heater.
  3. Attach a garden hose to the drain valve or use a bucket to catch the water. Be careful if it’s hot. Plastic or cheaper buckets or hoses might soften and you could get burnt.
  4. Run the end of your hose to a drain or out to your driveway.

4. Removing the Water Heater Control Valve

Time to remove your faulty gas valve. To do this:

  1. On newer models, there may be a pilot wire and a thermal fuse wire. Disconnect these first.
  2. Using a pipe wrench, carefully remove the water heater control from the tank. Some models might need a screwdriver and pliers to remove them.
  3. Once you have released the torque from the pipes, use your hands to uncouple them. This means you are less likely to damage the pipes.
  4. When you are applying torque to the connections to release them, hold the water heater control in place. That way you can avoid additional damage.

Quick Tip

Once you have removed the gas valve, it’s a good idea to take it with you to buy your replacement. That way you will be sure to get the right model.”

5. Attaching Your New Water Heater Control

Essentially you are going to reverse the steps you took to remove the faulty unit.

There are just a few things you need to think about when doing this:

  • Use Teflon pipe tape to ensure a good seal on the pipes when you reconnect. The correct color for gas supplies is yellow (2). The tape goes over the thread on the male pipe which then screws into the female pipe.
  • Make sure you don’t cross thread the pipes — you don’t want to damage your new water heater control or the gas pipe.
  • Thread the pipes by hand as much as you can and then tighten with your wrench or pliers. Make sure it’s secure and sealed but don’t overtighten.
  • Remember to reattach the wires if they are present.
  • Make sure you bleed any air from the system after refilling the tank with water. To do this, open the pressure release valve on the tank and let any air out. Next, turn on a hot water faucet until the water flows freely (the water will be cold at this stage).
  • Don’t relight your pilot and try and fire up your water heater until it’s been refilled.
  • Watch out for gas leaks; check for them before turning the pilot on. You will either smell it or you can check by spraying a mix of soap and water on the connections. If you notice any tiny bubbles, you have a leak.

If you detect a leak turn off the gas and either repair it yourself or call out your gas supplier.

Finishing Up

If you don’t find any problems and your water heater fires up, then in about 20 minutes you should have hot water.

Just remember, if you don’t feel confident enough to replace a water heater control yourself, call a professional to do it for you. Even if you are doing it yourself, it’s a good idea to check your manufacturer’s recommendations for your water heater.

We hope you found our guide useful and are now able to replace your gas valve. Please leave us a comment below with anything you think we’ve missed or your own experiences. Also, don’t forget to share.

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About the Author

Peter Gray

Peter has been a homeowner for 35+ years and has always done his own repair and improvement tasks. As a retired plumber, Peter now spends his time teaching others how they can fix leaks, replace faucets, and make home improvements on a budget.

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