Testing An Electric Water Heater Thermostat

While this DIY Repair blog has devoted articles to identify the reasons a gas water heater won’t heat and the proper way to vent a gas water heater, we haven’t spent much time addressing how to repair an electric water heater. This week, we’re taking care of that!

Let’s start with how electric water heaters heat the water. We’ll then show you, step-by-step, how to test a crucial component that determines how successful that heating process will be.

How an electric water heater heats the water

Most electric water heaters use two heating elements to warm the water in the tank. When thermostats installed in the tank detect the water temperature has dropped below a designated setting, the heating elements will cycle on, then cycle back off after the water temperature returns to the designated setting. Lower temperature settings will cause the elements to cycle on less frequently whereas higher settings will require the elements to cycle on more frequently. While the highest available temperature setting on electric water heaters is usually 150° Fahrenheit (66° Celsius), most manufacturers, including Rheem, A.O. Smith, Bradford White, Bryant, Carrier, Coleman, Honeywell, and Lennox, recommend the water temperature be set no higher than 120° Fahrenheit (49° Celsius).

Most electric water heaters use 240 volts of alternating current to operate both the upper heating element, located near the middle of the tank, and the lower heating element, located near the tank’s bottom. Each element is controlled by its own thermostat. The thermostats maintain the water temperature inside the tank by opening and closing contacts that allow voltage to flow to the heating elements. The elements are designed to cycle one at a time and, as noted above, the frequency of these cycles is determined by how much heat is needed.

What do I do if the water heater isn’t heating?

If your electric water heater is not heating the water, you should first determine if a house fuse has blown or a circuit breaker has tripped. If you’ve confirmed the water heater is receiving sufficient voltage, shut off the power to the water heater and check to see if the reset button on the unit’s high-limit thermostat has tripped. This button will trip if the water in the tank has been overheated. This can be caused by the thermostat contacts fusing closed, the thermostat is out of calibration, or by a shorted heating element. If the reset button has tripped, you should press the button and restore power to the water heater to see if that corrects the problem.

Is the water heater still failing to heat the water or does that reset button continue to trip? Then your next step is to use a multimeter to test each element and its accompanying thermostat for “continuity” – a continuous electrical path present in the components – or to determine if one of the elements has shorted. If an element or thermostat lacks electrical continuity or an element has shorted, the part is defective and will need to be replaced.

Testing a heating element is pretty basic. Shut off the power to the unit, remove the appropriate access panel, detach the power wires from the element, then touch one of the meters leads to one of the element’s terminals and the other lead to the second terminal. The meter display should indicate 10 to 30 Ohms of resistance if the element has electrical continuity. To determine if an element has shorted, touch one meter lead to an element terminal, and the second lead to the element nut or the tank itself. If the meter display indicates Ohms of resistance then the element has shorted. Testing an electric water heater thermostat is a little more involved.

How to test a water heater thermostat

Just as you would when testing a heating element, your first step is to shut off the power to the water heater. Now here’s how you should go about testing both of the unit’s thermostats:

  • Remove the upper access panel.
  • Move any insulation out of the way, then detach the protective cover.
  • Press the upper thermostat’s reset button to reset it if necessary.
  • Note the location of the power wires connected to the thermostat, then disconnect the wires to isolate the thermostat from the circuit.
  • Using a multimeter, touch one lead to a left-side terminal on the reset portion of the thermostat and the second lead to the other left-side terminal.
  • The meter display should indicate close to zero Ohms of resistance if the thermostat has proper electrical continuity.
  • Repeat the test on the right-side thermostat terminals.
  • Next, you should test the lower portion of the thermostat. Touch one meter lead to the common terminal and the second lead to the heating element’s upper terminal.
  • If the water temperature is below the designated setting, the meter display should indicate close to zero Ohms of resistance.
  • Move the second lead to the heating element’s lower terminal and the meter display should indicate no continuity.
  • If the water temperature is above the designated setting, the reverse will be true: the heating element’s lower terminal should show continuity and the element’s upper terminal should not.
  • To test the lower thermostat, remove the lower access panel, move the insulation out of the way and detach the protective cover.
  • Disconnect the power wires to isolate the thermostat.
  • Touch one meter lead to one of the terminals and the second lead the other terminal.
  • If the water temperature is below the designated setting, the meter display should indicate close to zero Ohms of resistance.
  • If the water temperature is above the designated setting, the meter display should indicate no continuity.
  • An opposite reading means the thermostat is defective and will need to be replaced.
  • With testing complete, reconnect the power wires to the appropriate terminals, replace the protective covers, realign any insulation, and reinstall the upper and lower access panels.
  • Restore power to the water heater.

Find the right part to keep the hot water hot at Repair Clinic

Did your troubleshooting reveal a faulty thermostat or heating element? Then you’ll need to find the right thermostat or element that matches your water heater. The Repair Clinic.com website has already correlated all the data to keep this part of the repair process simple. All you have to do is type the full model number of the water heater in the website’s search bar, then use the “Part Category” and “Part Title” navigation filters to select the appropriate part to display the exact genuine OEM component that works with your unit.

As your repair partner, Repair Clinic can assist you in repairing the water heater yourself. Check out the “Videos & Articles” or “Repair Help” website sections to find troubleshooting and part installation videos, step-by-step guides, schematics, diagrams, and articles to help you keep the hot water flowing.

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