How To Test Thermostat On Water Heater

San Rafael

(415) 942-6565

Santa Rosa

(707) 452-3464

One of the many pieces of advice you have probably heard when it comes to at-home water heater service and repair is to test your water heater’s thermostat. But you may be confused as to how to actually go about performing a test on a thermostat. While there are many steps to the process, it can be accomplished quickly and easily.

Electric water heaters are heated through one or two heating elements that thermostats control. The thermostat not only controls the temperature of the tank, but also how the heater operates. Setting the temperature lower will result in the heating elements running less to heat the water in the tank, whereas a higher setting will cause them to cycle more frequently. In order to maintain the water temperature inside the tank, they open and close the contacts that allow voltage to pass to the heating elements. They will also usually have a safety feature where they can prevent overheating in the water tank. It depends on the type of water heater, but there will typically be an upper thermostat that powers the upper heating element, and then a switch to the lower thermostat to signal the lower heating element to heat the rest of the water.

Gas water heaters work similarly to electric water heater thermostats, but instead of sending signals to the heating strips or coils, they send signals to open the gas valve to ignite the burner for the water heater. Older water heaters have a knob on the front, typically to control the temperature of your water heater. When the water dips below the programmed temperature, the water heater signals to open the gas valve and ignite the burner to heat the water again.

If you find that you are not getting any hot water, it is possible that your electric water heater thermostat is not working. In today’s article, we will look at the best way to test for a malfunctioning thermostat, including the signs that you need to investigate the thermostat, what tools you will need and how to prepare, and each of the steps in the thermostat testing process.

Signs the Electric Water Heater Is Not Working

Depending on the specific problem you are experiencing with your water heater, it will be a problem with a couple different parts of the thermostat. If you are getting no or not enough hot water, it is probably an issue with the upper thermostat. Slow hot water recovery can be an indication of a faulty lower thermostat. If the water is too hot, it is likely that one or both of the water heater thermostats are set too high. Finally, if the high-limit switch continuously trips, this could mean that the upper thermostat is possibly malfunctioning and letting your water become heated far beyond safe levels, therefore tripping the high-limit switch, popping out the reset button, and requiring a reset.

If you are experiencing any of these troubles with your hot water heater, it is possible you could have a thermostat problem. The next step to take is to test your thermostat to rule out if it is the problem or not.

Testing Your Electric Water Heater Thermostat

The only tools you will need for this job is a digital multimeter and a flathead screwdriver. You may also want insulation, tape, and a replacement thermostat, but these are not required.

Before you begin your thermostat test, be sure to turn off the power supply to the water heater by switching the circuit breaker off. Even after you have shut off the power, double check the electricity is to make sure there is no voltage that can harm you while you work. You can use a voltage tester or multimeter to check for this. After this, you are ready to go through the steps to test your hot water heater thermostat.

1) Remove Access Panel

Locate your water heater thermostat by referring to the manual instructions for your specific system. You can use the flathead screwdriver to remove the panels for both the upper and lower thermostats. There may be a layer of insulation over them as well, behind the access panel, that you can fold away and tape down while you work.

2) Set Multimeter

Use the dial to set your digital multimeter to the lowest ohms of resistance. Be sure to have the multimeter’s instructions on hand to make sure you have the correct guidelines for whichever model you have so that you know the correct way to bring the setting down to the lowest ohms of resistance for your thermostat test.

3) Prepare Upper Thermostat

Before performing the test for the upper thermostat, start by checking the reset button, which indicates when the tank overheats, to make sure you don’t have to do a reset for the tank. Then, loosen the screw terminals and disconnect the wires so that you can isolate the thermostat from the system. As you disconnect the power wires, be sure to have a way of remembering where they are so that you can reconnect them once you are done.

4) Upper Thermostat Test

Put one probe from the multimeter on the reset terminal (beside the reset button) and the other probe on the left side terminal, which will be the one with power wires. If the multimeter’s reading says 1, then the water heater thermostat most likely needs to be replaced. If it reads 0, it is functioning normally. Repeat this with the right side terminal.

After this, you can check the water temperature and compare it to the temperature set on the water heater thermostat. Place one multimeter lead on the left common terminal for the lower thermostat, then move the other lead to the upper heating element terminal. If the first reading says 0 and the second reading says 1, your water temperature is lower than it should be. Now move the second lead to the lower heating element terminal while keeping the first lead on the left common terminal. If the first reading is 1 and the second is 0, the set temperature is higher than it should be.

5) Lower Thermostat Test

The testing process will be performed similarly with both the upper and lower thermostats on most water heaters. Place the leads in the two terminals as you did with the upper one. If the reading is at or around 0 ohms, then the water temperature is lower than it should be, and if the reading is 1 ohm, that means there is no continuity, meaning no heat regulation.

Next, you can compare the data from both tests on the upper and lower thermostats. If the upper and lower thermostats have an opposite reading from one another, that means the lower thermostat needs to be replaced.

6) Replace Electric Water Heater Thermostat

Once you have found the faulty thermostat, it is time to go about replacing it. You will need to make sure you find a replacement water heater thermostat that is compatible with your particular electric water heater. For instance, if you have two heating elements instead of one, you will need thermostats that specifically work separately for the two elements. After that, there should be instructions in your owner’s manual for setting it up. Once installed, set your desired water temperature.

7) Heating Elements Tests

If your thermostat readings are normal, that means there is another factor causing problems with your water heater. This could be a faulty water heater element, which is a problem within water heaters that can show similar symptoms as a faulty thermostat. Testing a heating element is similar to testing the thermostats: shut off the power, remove the protective cover, detach the power wires, then put one lead against one heating element terminal and the other against the second terminal. The reading should show 10 to 30 ohms of resistance. You can also test if an element has shorted by touching one lead to an element terminal and the second lead to the element nut, or the water heater’s tank. The element has shorted if the display reads 0 ohms of resistance.

8) Restore Water Heater

After you have completed your thermostat test and/or replacement, reconnect the power wires as they were and place the protective covers back over each of the thermostats, securing the access panels. Also, don’t forget to turn the power to the water heater back on. Test the hot water to see if the temperature feels correct now with the new thermostat in place.

Replacing and Repairing Electric Water Heaters

If the problem lies beyond the water heater thermostat or heating elements, you could need professional help with repairing or replacing your water heater. Hiring an experienced technician is important when something like a short circuit occurs to affect the wiring of the water heater, since this repair work can be incredibly dangerous. John Owens Services is a professional plumbing company you can rely on for dependable repair work and replacements for any electric water heater, water heater thermostat, heating element, and more. A functioning hot water heater is essential for any home, so any problems that pop up should be taken care of as soon as possible. John Owens will make sure that every element in your water heater is functioning to perfection so that you don’t have to worry about low-hot water or faulty thermostats.

Testing your water heater’s two thermostats can be an easy way to get to the bottom of a water heater problem. If you are able to identify an issue with one of the thermostats once you start to notice signs of water heater failure, you can quickly fix your water heater simply by installing a new thermostat. By following the process described in this article, you can save time and money on your water heater diagnosis and repair process.

Need Help?

We’re open Monday – Friday 7:30am – 5:30pm, call today or schedule online now!

Serving Marin & Sonoma Counties

Good plumbing, heating, and air conditioning systems are vital in every North California home. John Owens Services, Inc. is proud to be the expert plumbing company you can count on

The John Owens Way

Our philosophy is simple, we always want to maintain equipment to give it the longest life possible. Next, we want to focus on repairing when something goes wrong. Then only as the last choice, we replace equipment when needed. That’s the John Owens Way.

San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464



Regular maintenance keeps your home’s systems running well all year long. We’ll help you gain efficiency and save money.



When something breaks down, our team will get to you fast. We’ll find the problem and fix it to get you back to normal.



When it’s time to replace something in your home, we’ll help you get a top quality product that matches your specific needs.
San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464