Test & Replace a Water Heater Thermostat: DIY Guide

replace thermostat

At some point in time, we will likely all be faced with a water heater that’s not producing any hot water. We can either call a licensed plumber or fix it yourself. Fortunately, most water heaters can be repaired relatively easily. There are really two main causes of a water heater failure; one is the heating elements and two is the thermostat.

If you haven’t tested or replaced a water heater thermostat before, it can seem like a daunting task. It’s really not too hard. Fortunately, the process is relatively straightforward if you have someone knowledgeable guiding you and a few basic tools. 

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If your water heater is not producing hot water, we need to test the water heater thermostat and replace it if needed. In this article, we will look at how to troubleshoot your electric water heater thermostat and how to replace it if needed.

How Electric Water Heater Thermostats Work

When you start to notice that your water heater isn’t working as it should, the thermostat is more than likely the problem or at least part of the problem. There’s no need to replace the whole heater if you can save yourself time and money with a simple thermostat replacement. It only takes a few minutes once you’ve read through the following steps.

Electric water heater thermostats work by opening and closing contacts that allow electricity to flow to the heating elements. The heating elements are designed to cycle on and off depending on demand.

All modern residential water heaters have two heating elements and two thermostats. There are two panels located on the side of your electric water heater, each of which houses a thermostat and heating element.  The upper thermostat is different from the lower thermostat. The upper thermostat is larger and controls the lower thermostat.

Rarely do both thermostats fail at the same time (although I do recommend replacing both when one fails).

When an upper heating element or thermostat fails, the entire water heater stops producing hot water. When a lower heating element or thermostat fails, the top thermostat and element will continue to heat water in the upper half of the tank, but you will notice the hot water quickly runs out or is only lukewarm.

Are Electric Water Heater Thermostats Universal

No, all water heater thermostats are not universal. There are some variances in thermostats between single element water heaters and dual element water heaters. Also, in dual element water heaters, there is a difference in the upper and lower thermostats.

When shopping for a water heater thermostat you need to know how many elements the water heater has and the voltage. You can find this information on the data tag on the side of the water heater.

If the data tag is missing, you can identify single element vs dual element by the number of access panels on the water heater. You can find the voltage written on the end of the heating element. Common residential dual element water heaters are 240 volts.

There are more than 50 brands of residential tank-style electric water heaters on the market and the thermostats are designed to interchangeable on most models. You should read the product description carefully when purchasing.

Dual Element Thermostats

water heater thermostat

This photo shows a set of upper and lower thermostats for a typical residential water heater.

The thermostat on the left is the upper thermostat and includes a high limit switch identified by the red reset button.

The thermostat on the right is the lower thermostat.

For a replacement kit containing 2 heating elements, upper and lower thermostats, and seals we recommend the Rheem SP20060 Electric Water Heater Tune-Up Kit available at Amazon.com.

If you only prefer to only purchase the upper thermostat see the Rheem UV11698 UV11698-Thermostat-Electric. It’s a universal upper thermostat manufactured by Rheem.

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If you only need to purchase a lower thermostat see the Rheem SP11695 Electric Thermostat. It’s a universal lower thermostat manufactured by Rheem.

Single Element Thermostats

The thermostat pictured here is designed for a single element water heater.

The thermostat closely resembles an upper dual element thermostat but the difference is in the number of wire terminals.

As you can see the single element thermostat only has two terminals on the right side and four on the left side.

If you need to purchase a single element thermostat see the Camco 07843 Single Element Water Heater Thermostat with HLC. This is a universal single element thermostat with a built-in high limit switch.

Necessary Tools and Preparation

Here’s a list of the materials you’ll need:

  • 1/4 inch nut driver or Flathead Screwdriver
  • #2 Phillips screwdriver
  • Analog or Digital Multimeter/Voltmeter
  • A replacement thermostat

How to Test a Water Heater Thermostat for Continuity – Step-By-Step

We need to check the thermostats for continuity. This will determine if the thermostat has failed. To do this you will need an analog or digital multimeter.

WARNING: Working with electricity is very dangerous and can kill you. Be sure the power is OFF before doing any work with wiring and electrical connections.

Use these steps to figure out which thermostat has failed.

Step 1: Turn the power off

Head to your circuit board and turn off the water heater’s breaker. Locate the breaker inside the panel box labeled “water heater” or “hot water” and turn the breaker off.

Step 2: Remove the outside access covers

Use a 1/4 inch nut driver or flathead screwdriver to remove the upper and lower thermostat access panels. Fold back the insulation over the thermostat. Use tape to secure the insulation out of the way. Remove the interior plastic covers over the thermostat.

Step 3: Confirm power is off to the water heater

Before handling anything on the thermostat use a multimeter to confirm the power is off to the water heater. If you have a voltage stick you can use that as well.

Using the multimeter connections, touch the top to legs at the same time. The meter should read 0. With the black connector touching the water heater, touch each leg to confirm there’s no power.

Step 4: Check the high limit reset button

Check to see if the high limit reset button has tripped. Sometimes this button will trip if:

  • the thermostat contacts have fused closed.
  • the thermostat is out of calibration.
  • the heating element has failed.

Step 5: Disconnect the wiring

Using your phone or a digital camera, snap a picture to provide a reference if needed to identify which wires are connected to which terminal. Using a #2 Phillips screwdriver, disconnect the wiring to each terminal on the thermostat.

Step 6: Check the thermostat with a multimeter

Using an analog multimeter, set the multimeter to the lowest ohms of resistance (typically x10). Calibrate the meter by pinching the probes together and adjusting the needle to 0.

Using a digital multimeter, set the multimeter to the lowest ohms of resistance, (typically 200) or if your meter has resistance with tone use that option.

Take one of your multimeter’s black probe and place it on the left side screw terminal. Take the red probe and place it on the other left side terminal. If the terminal has continuity, the meter should read close to zero. If it doesn’t, the upper thermostat is failed and needs to be replaced. 

Repeat this process for the right side terminals and the element terminals. See the above video for a demonstration.

If the upper thermostat is fine, you’ll need to repeat these steps for the lower thermostat and element.

Once you’re done testing your water heater thermostat, you can reconnect the wiring and close up the access panels or proceed to the steps to replace your thermostat.

If you’ve determined that your thermostats do not need replacing, you can check your heating elements next. We have another step by step article to do that at How to Test and Replace a Bad Water Heating Element.

How to Replace a Water Heater Thermostat – Step-By-Step

Once you’ve determined which thermostat is defective, it’s time to start the removal and installation process. 

Insider’s Tip: As mentioned earlier, it is generally a good practice to replace both thermostats and heating elements. The reason is that if one of the heating elements is starting to fail, it could short out the new thermostat shortly after it is installed.

Fore safety, some of the steps will be repeated here. If you followed the testing instructions above you can skip to Step 5. We will be recapping the preliminary steps first for those not testing their thermostats. Here we go.

Step 1: Turn the power off

Head over to the circuit breaker box and locate the switch that’s labeled ‘Water Heater’ or something similar. Turn it off, ensuring you turn off both switches if it’s a 220v switch. If you aren’t sure which one is the water heater due to old stickers or labels, contact a professional to switch them off for you.

Step 2: Remove the outside access covers

Remove the panel that corresponds to the thermostat that needs replacing. The panels are usually on the left or right side of the water heater unit. Use the 1/4 inch nut driver or a flathead screwdriver for this part, ensuring you don’t lose the small screws. Take out the insulation and remove the plastic protective cover that rests over the thermostat.

Step 3: Confirm power is off to the water heater

Use your multimeter/voltmeter to test each wire. You can do this by grounding out one of the lines and individually testing each wire or the screw that it’s under. Even though you’ve turned out the power at the circuit breaker, you should always double check your work using one of these meters to avoid electrocution.

Using the multimeter connections, touch the top to legs at the same time. The meter should read zero. With the black connector touching the water heater, touch each leg to confirm there’s no power.

Step 4: Disconnect the wiring

Using your phone or a digital camera, snap a picture to provide a reference if needed to identify which wires are connected to which terminal. Using a #2 Phillips screwdriver, disconnect the wiring to each terminal on the thermostat.

Step 5: Remove the defective thermostat

Using a finger or a flathead screwdriver, gently remove the old thermostat by pressing outward on the clips and lifting to thermostat up and out of the retaining bracket. Be careful not to break the retaining bracket. Breaking this retaining clip could require your water heater to be replaced.

Step 6: Insert the new thermostat

Place the new thermostat in the same location by inserting it into the retaining bracket that holds the thermostat in place. Reconnect the wires back into their proper places. Use your photo you took earlier as a guide if needed. Be sure that each wire is firmly connected.

Be sure the thermostat is resting firmly against the water heater because if not the thermostat may not function properly.

Next, set the thermostat to your desired temperature. We recommend a maximum temperature of 120 degrees Fahrenheit. You can use the flathead screwdriver to make these adjustments. This temperature setting is important because anything higher can become a scalding hazard for young children or the elderly.

Insider’s Tip: If you plan to replace your heating element with your new thermostat, you’ll need to drain the water heater. Some suggest a fast change without draining the tank, however, I do not recommend this because any error could damage the interior of your home. For draining your water heater and other maintenance tips see our article Water Heater Maintenance Tips for Gas and Electric Tank Water Heaters.

Step 10: Reattach the cover panels

Now that you’re all done with the replacement, it’s time to seal everything up and check your work. Replace the plastic protective cover and insulation. Reattach the exterior access panels.

Step 11: Turn the power back on

Now that everything is connected and in place, go back to the electrical box and turn the breaker back on. It’ll take approximately one hour for the tank to fully recover, but you should start getting hot water within 15 minutes. Be sure to check the water heater periodically over the next few days.

Final thoughts

That’s all there is to it! Water heaters aren’t too challenging, and replacing a thermostat can be done in a few minutes once you know what you’re doing. 

The key is to avoid taking any shortcuts, as dealing with electrical equipment can be dangerous. However, using the proper techniques and tools will make sure your water heater thermostat replacement is a quick and safe procedure.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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