How to Test Your Hot Water Heater Thermostat (5 Step Guide)

Last Updated On May 24, 2024

Updated on May 13, 2022



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How to Test Your Hot Water Heater Thermostat (5 Step Guide)

How do I test my hot water heater thermostat? 

The two main reasons why water won’t get hot in the water heater are a faulty thermostat or a faulty element. You need to test the hot water thermostat to determine the problem and take the correct steps to resolve the problem. 

In this PlumbingNav guide, you will learn how to test your hot water heater thermostat yourself. 

What's In This Guide?

      How to Test Hot Water Heater Thermostat

      Step 1: Check the Reset Button

      First, you want to see if the reset button has been activated. If it has, you may only need to reset the thermostat. See below to learn how to reset the thermostat. 

      If the reset button wasn’t triggered, you should continue testing the thermostat. 

      Step 2: Turn Off the Power

      Turn off the power to your water heater. You can do this by turning off the breaker in the circuit box. Hopefully, you had the foresight to label everything clearly. 

      Step 3: Locate and Inspect the Thermostat

      Next, you need to locate the thermostat. You will find the thermostat under the access panel on the water heater tank. Remove the access panel with a screwdriver and move any insulation out of the way. Check for visible signs of damage. After you check for damage, restore power to the unit. 

      Most family water heaters over 30 gallons contain two heating elements to increase efficiency, meaning there will be two thermostats: upper and lower. It can be helpful to learn which thermostat failed. 

      If the upper thermostat fails, you will not receive any hot water at all. If the lower thermostat fails, you will get limited hot water or water that never gets fully hot. If both thermostats go out, you will not receive any hot water.


      Step 4: Find a Multimeter

      You will need a device called a multimeter to test your thermostat. A multimeter measures electricity. You may have either an analog multimeter or a digital multimeter. Most multimeters offer the option to measure voltage, amperage, and resistance. 

      Before you test your thermostat, you should ensure your multimeter works. One way to do this is to test it on a 9volt battery. Ensure you are measuring volts and attach the leads to the battery. 

      The red lead should touch the positive terminal and the black lead should touch the negative terminal.

      Step 5: Test Both Thermostats

      Now, you are ready to test the thermostat for continuity with your multimeter. Continuity refers to a regular electrical current in the device. If the unit has no continuity, it isn’t working. 

      Test the upper thermostat first. Ensure the upper thermostat is set to the highest heat setting before testing, and ensure the lower thermostat is set to the lowest heat setting. You can do this by using your screwdriver or using the digital controls, depending on your water heater.

      Set your thermostat to read voltage. Now, place both leads on the two terminals to the left of the red reset button. Repeat the test on the right-side terminals. You want the multimeter to read 240 volts.

      Don’t forget to test both thermostats. Before testing the lower thermostat, you need to turn the upper thermostat to the lowest heat setting. Ensure the lower thermostat is set to its highest setting. Once again, you want the multimeter to read 240 volts.

      Step 6: Analyze Your Findings

      Now, you need to determine what your tests told you. Keep in mind that a majority of the time, the elements will be at fault as opposed to the thermostat. Once you know whether the problem lies with the thermostat or element, you can move forward accordingly. 

      Read below to learn how to troubleshoot your thermostat.

      FAQs for How to Test Your Water Heater Thermostat

      How do I troubleshoot my electric water heater thermostat?

      You tested your electric water heater thermostat, and it’s not working properly. What do you do now? Here are some tips on how to troubleshoot the electric water heater. 

      Verify temperature 

      Sometimes the temperature on the thermostat isn’t at the correct setting. When this happens, all you need to do is set the thermostat to the temperature you want it at (most experts recommend 120 degrees). 

      Check both thermostats to see the temperature. If the temperature isn’t where you want it, simply change it. Most thermostats allow you to change the temperature digitally. This makes it easy to read, and you can do it with the press of a button. Just make sure you set both thermostats and not just one. 

      Keep in mind that if the setting reads 120 degrees, but it doesn’t seem to heat up to that temperature, turning the temperature up even higher will not help. 

      Replace thermostats

      If you need to replace the thermostat, you should replace both the upper and lower thermostats. Most dual-element water heaters require 240 voltage but check your user manual to verify the correct voltage for your unit. 

      To replace the thermostat yourself, simply detach all wires from the original one and take it off. Place the new one in its place and carefully reconnect. You will then set the thermostat to the desired temperature and turn the power back on. Wait 1 – 3 hours to test the hot water. 

      How do I reset my water heater thermostat?

      Sometimes, the water heater isn’t working due to the reset button getting triggered. 

      Electric water heaters come with a reset button that shut off power when in contact with a power surge or excessive moisture. First, locate the reset button. In most cases, it’s red and located near the thermostat. 

      Be mindful if your water heater has two thermostats- both will have their own reset button. 

      If you use a hot water heater timer switch check the schedule to ensure it’s accurate. If everything seems to be fine but the problem keeps happening, call a professional. 

      What trips the reset button on a hot water heater?

      The reset button shuts down the power for a reason- usually due to a power surge or a thermostat malfunction. This safety feature prevents the hot water heater from potential damage. 

      However, there are numerous reasons a water heater thermostat can require a reset seemingly out of nowhere. Some of the main reasons include:

      • Excessively hot water
      • Bad thermostat
      • Bad reset button
      • High limit switch failure
      • Short
      • Loose wire

      If your reset button continues to trip over and over again, lower the setting on your water heater. The reset button usually trips at 170 degrees. You can also try testing the thermostat. If that still doesn’t resolve the problem, it may be time to call a plumber.

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      About Plumbing Navigator

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      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

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