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How to Test A Water Heater Thermostat

By July 22, 2021Water heater
water heater thermostat

The water heater provides hot water for the house. The hot water is used in washing machines, dishwashers, and the shower. We always want our water heater to work well because who likes freezing cold showers? However, sometimes, the water heater may go out. It can be one of two things: heating element or thermostat. Start first with testing the thermostat.

How to test the water heater thermostat? Well, there are two thermostats on a water heater. One above and one below. You need to use digital multimeter tools to test it.

The good thing is if it is the water heater thermostat, then it does not take long to repair or cost a lot.

What Does a Water Heater Thermostat Do

There are two heating elements in a standard 30-gallon water heater tank. Each element contains a water heater thermostat. The thermostats are used to produce heated water for the various purposes needed within the home.

One thermostat will control the temperature of the water at the top of the tank while the lower thermostat helps heat the newly entered cold water. The thermostats also control the current that moves from one element or thermostat to the next.

How to Test a Water Heater Thermostat

The first thing you need to do before you attempt any work on your water heater is, turn the power off. Next, you will remove the access panel, the insulation, and the plastic protective covering. After doing this, you will touch one of the probes from your digital multimeter to the ground metal (for example, the unpainted metal tank).

Then, touch the other probe to each of the thermostat terminals, and both heating element terminals. The multimeter will indicate, no voltage or “zero” at all times. This confirms you are showing no power to the unit and can continue your testing of the water heater thermostat.

Here is a video that tells how to test a water heater thermostat with a digital multimeter.

How to Change Out a Faulty Water Heater Thermostat

It is very easy to change out a faulty thermostat.

  1. First, you will turn the power off to the unit.
  2. Then, you will remove the outside covering and insulation.
  3. Take your digital multimeter to verify that the power is completely off.
  4. Once you have determined the power source is dead, you may begin unscrewing the thermostat and disconnect the wiring.
  5. When you have the thermostat off and out, you can replace it with a new one.
  6. Remember to connect the wires the same way you removed them and reattach the new thermostat screws.
  7. After the installation is completed, you may turn the power back on and check that it works properly.

Water Heater Thermostats Are Not Universal

Not all water heaters are built the same. Some water heaters have two heating elements and others have one heating unit. These are not the same, so you will want to make sure you purchase the correct type for your water heater.

Also, in dual-element water heaters, the lower and upper thermostats are not the same and cannot be used interchangeably. The upper thermostat is larger, has more terminals than the lower, and it controls the temperature of the water. Check out the pictures below of the dual element and single element and a better explanation of the two.

It’s always a best practice to check the information tag on your water heater to make sure you purchase the correct thermostat. There are dozens of residential electric water heater manufacturers and most can use OEM parts, but taking a few extra minutes upfront can save you time, money, and frustration later.

Dual element thermostat

Dual Element Vs. Single Element Thermostats

There are dual element and single element thermostats. A typical water heater has two heating elements, so a dual element thermostat is needed. The upper unit has a high limit switch and red reset button, while the lower unit is basic. The good news is if you have to replace one, you don’t have to replace both at the same time. The dual element thermostats are about $55 each or more.

Single element thermostat

Single element thermostats are for using with single heating water heaters. They average about $20 each to replace. If you aren’t sure how to replace them, don’t be afraid to contact a professional.

Purpose of the Water Heater Reset Button

On the dual element water heaters, there is a reset button. The purpose of this button is to stop the power from getting to the water heater and making the water too hot. This button does this when there is a problem, such as a broken thermostat. If you try to reset it and it switches off, there is a problem and you need to contact a professional.

Bradford water heater label
Bradford water heater label

Age of the Water Heater is Important to Know

Gas water heaters usually last about 8-12 years, while electric is 10-15 years! Many manufacturers will have the date listed on the label as to when it was made. However, there are manufacturer’s whose labels are not as easy to read, such as the Bradford White water heaters and you will need to know how to read the label.

Other Maintenance

There are four ways to maintain the water heater: Flush the hot water heater, adjust the temperature and reset, and turn gas water heater off and back on. Lastly, there are some hot water maintenance tips you can do as well that will be discussed further.

Water heaters do a good job working on their own without much maintenance. However, the TPR (Temperature Pressure Relief Valve) or T&P it is also called, is one area you want to check annually. This is because the TPR valve releases pressure in the water heater and without it, the water heater can explode!

  1. Check that the connection from the TPR valve and tank is not corroded
  2. The valve is not leaking water
  3. There is an extension pipe of the TPR valve within 6 inches of the ground and it points down. The discharge tube must be made out of an approved material, such as copper or CPVC. Without this tube, you could be burned by water that is over 210 degrees!
  4. Contact a professional if you have any concerns or need assistance.

Lastly, when checking your water heater, make sure there is no mold growing on the concrete. This could be a sign that there is a leak from the water heater or from another source. You will need to find out what is causing it so it does not spread and clean it up safely.

When to Call a Professonal

Anytime you are working with electricity as a homeowner, it can be important to consult a professional. You will need a couple of screwdrivers, pair of pliers, and a digital multimeter. If you do not have access to any of these tools, it is recommended to call a professional. Additionally, if you are unsure of how to test the water heater thermostat, a professional is trained to help.


When our water heater stops working, it can actually be a good thing because it stops the flow of water to the heating source. We don’t want the water coming out in the shower, tub, or sink scolding hot and burn someone. Thank goodness this safety measure is in place. On the other hand, it can be frustrating trying to figure out why it isn’t working and testing the thermostat is the first place to start. All Coast Home Inspections can check out your water heater during a home inspection in Houston, TX.

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