How To Replace A Water Heater Thermostat

Most electric water heaters made today use a dual element system. Older units and some small models still being manufactured use a single element. For each element, the unit requires a matching thermostat, so dual element units have two thermostats, and single element models only one. When replacing one thermostat, it is a good idea to go ahead and replace both the upper and lower thermostats.

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Testing the Thermostats on a Dual Element Water Heater

Since most electric water heaters use both an upper and lower element, the process outline below is for them. To test, you will need a multimeter and screwdriver. You can pick up a good inexpensive multimeter online or any local hardware store.

Testing the UPPER thermostat:

  1. Turn off the power to the water heater.
  2. Remove the access panels to the elements along with the insulation underneath.
  3. Use a screwdriver to set the upper thermostat to its highest setting.
  4. Set the lower thermostat to its lowest setting.
  5. Turn the power to the water heater back on.
  6. Make sure there is voltage coming into the water heater by checking the 2 wires above the reset button. It should read 240 volts.
  7. Use your multimeter to check for power on the upper element terminal screws. If no power, this thermostat is bad and needs to be replaced. If there is power, test the lower thermostat.

Testing the LOWER thermostat:

  1. Set the upper thermostat to its lowest setting.
  2. Set the lower thermostat to its highest setting.
  3. Make sure there is voltage on the lower element. If the multimeter shows power at the element, allow a few minutes for the water to heat up.
    • Lower the temperature on this thermostat and wait for an audible click which indicates the thermostat is functioning correctly.
  4. If there is no voltage at theĀ element, test the lower thermostat for power.
    • Place one of the multimeter probes on the top contact screw and the other probe on the metal casing of the water tank. It should show a reading of ~120 volts.
    • If there is no reading, the upper thermostat will need replacing since it provides voltage to the lower thermostat.
    • If there is a reading, place one probe on the lower contact screw and the other probe on the metal casing of the water tank. It should show approx. 120 volts. If not, the lower thermostat will need to be replaced.

Electric Water Heater Thermostat Replacement

Step 1

replace-electric-thermostat

Always disconnect the power or shut off the breaker before doing any work on a water heater. To change thermostats, you will need to remove the access panel and safety cover (do this for both upper and lower access panels on dual element units). For the sake of safety, use a voltage meter to make certain the power is off. Make a simple diagram of how the wires are connected to the diagram. Remove the wires from the thermostat.

Step 2

Thermostats are held in place by a special bracket that holds it firmly against the tank, allowing the thermostat to sense the internal water temperature. Gently pry out one side of the bracket while twisting that side of the thermostat upwards to prevent the bracket from locking in place again. Repeat for the other side. Repeat for the lower thermostat on dual element models.

Step 3

Take the old thermostat(s) with you to purchase a replacement. While most thermostats are interchangeable, the best results come from accurately matching the components.

Step 4

If the bracket was damaged during thermostat removal, you can get a replacement bracket as well. The old bracket can be pried upward to remove it and the new one can be placed flat against the tank and slid downward until it lock into place.

Step 5

Replace each thermostat by sliding it evenly downward into the holding bracket until it locks in place. Replace the wiring exactly as it was removed. Replace the safety cover(s) and access panel(s). Restore power and allow the water heater to work for one hour before testing the hot water.

If you suspect a heating element has also gone bad, seeĀ How To Replace A Water Heater Element.

Gas Water Heater Thermostat Replacement

Gas water heaters use a different type of thermostat system. On most gas water heaters, the gas control valve, which includes both a thermostat and a heat limiting device, are located on the outside of the unit, near the bottom. It can be identified as the component with the controls for temperature and the pilot light.

If the thermostat on a gas water heater goes bad, you will have to replace the gas control valve component.

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7 thoughts on “How To Replace A Water Heater Thermostat

  1. I have a 50 gal rheen that has been in our home and used since 2003 with rainwater only I replaced the thermostat 2 times but my wife says go to 0 before it turns on. I disagree, I think it 80 to 90 degrees. We live on Saipan NMI so the daily temp is 75/8 to 89 to 91 F. I say the turn on temp. is preset and the only adjustment is high temp.
    Thank you for your swift reply

    • You’re correct. Typically the lowest temperature setting on a water heater is about 80-90 degrees. Each model is different though and some have very basic temperature presets. Some models have a “vacation” mode where it will keep the water at about a 50 degree minimum to keep it from freezing in case really cold weather. Probably something you’ll never have to worry about in your area.

  2. I am replacing fuses on my water heater daily, I noticed that the part of the fuse that is screwed in to panel is a light brown. At first I was changing the fuses about once a month now it is everyday, any ideas, a friend told me it was most likely the thermostat. Being that we have hard water and a high iron count in the soul, our well water is red at times

  3. More likely clogged/corroded elements. Sounds like the thermostat is not turning off, which requires heat, which clogged and corroded elements have difficulty delivering. There are kits at the home center to replace both thermostats and elements for less than 40 dollars. While you’re in there, might as well replace them all, given the duty cycles the current thermostat is undergoing until a fuse blows.

  4. It appears that only one thermostat is working on my water heater and one of my water heater breakers will not reset
    any suggestions ? on why a breaker would trip and not reset ?

  5. I have no leaks or indication of rust. Our gas water heater seams to be working fine, it’s turning on okay, running for a while but the amount of hot water it produces seams like it’s getting lower and lower offer the last two months. The unit is 14 years old but has never seemed to have a problem until now. We run a water softener with it. What is likely happening to cause it to have heating problems?

    • Nick,
      There is a plastic supply feed tube that goes from the inlet to the bottom of the tank. The hot water rises and comes out the top of the tank. The cold feed water is suppose to go to the bottom of the tank where it will get warmed by the flames or heating elements. If the plastic feed tube cracks, breaks, or just comes apart ….you are mixing cold water into your hot water at the top of the tank (the water that is going to your faucets). Hardware and even big box stores like Home Depot and Lowes will have this pipe. Replace this inexpensive tube and you will have hot water again!.
      Turn off your gas, and the water inlet and outlet valves. Drain the tank part way (you should do this once a year anyway). Disconnect the cold water line and lift the tube out. Odds are it will be very short or non existent. if the tube fell off, don’t worry it wont hurt anything – leave it in the tank but you must remove the metal fitting at the top. Drop the new tube into the hole – reconnect the cold line – and turn the water and gas back on. Restart the water heater. Done.

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