How to Replace an Electric Water Heater Thermostat

Instructions on how to replace an electric water heater thermostat. Find out how it works, problems associated with the thermostat failure, and how to avoid some issues.


How does a thermostat work

Water heater thermostat

Every electric water heater is equipped with one or two thermostats designed to set and control the temperature, and turn the heating element ON or OFF.

Upper and lower thermostats control upper and lower heating elements. If the electric water heater is not producing any hot water or the temperature is not as requested (set), some testing must be performed to determine which thermostat is bad.

Furthermore, the thermostats will allow one heater to work in a simultaneous mode, so they heat water at the same time or non-simultaneous mode. Water heaters thermostats are surface mounted and are firmly attached to the side of the tank. Any looseness will affect the normal operation.

These are designed to sense the heat through the tank surface and set the temperature. As part of the thermostat is the ECO or high limit switch (if applicable), which protects the unit and users from extremely high temperatures.

How to change the temperature on the thermostat

The hot water temperature inside the storage tank is factory set at 120 F as a safety precaution, so by using a dial, you can easily change the output temperature. If you increase the temperature setting above the factory pre-set temperature, there will be a danger of scalding injuries, and heating might not be economical. The time needed for scalding burns or serious injury is as: if the temperature is set at 120 F, it takes more than 5 minutes to produce injuries, for 140 F less than 5 seconds and 160 F about half a second.

  • Before you change the temperature on the water heater thermostat, make sure that the electrical supply to the unit is turned OFF.
  • Once the power is OFF, remove the cover for full access to the thermostat.
  • Use the screwdriver and rotate the adjustment dial clockwise to the desired temperature.
  • Bring the cover back and turn the power ON.

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How to replace an electric water heater thermostat (video included)

The procedure of replacing a water heater thermostat applies to either the lower or upper element.

  • Before replacing a thermostat, make sure that the electrical power to the unit and breaker is turned OFF.
  • Remove the cover and insulation to have access to the thermostat. Remove the plastic cover.
  • Make sure that there is no electrical power to the heater by using the voltmeter.
  • Disconnect wires from the thermostat. Make sure they are marked, so you don't have to guess when reconnecting.
  • Remove the thermostat from the mounting bracket.
  • Use a stiff brush and remove the scale and debris from the tank surface.
  • Now install a new and identical element, so the back of the element is flush with the tank surface. Keep in mind that the improper mounting will result in an incorrect water heating operation.
  • Refer to a wiring diagram located on the cover to reconnect the wires.
  • Bring the cover and insulation back and resume the power.
  • Adjust the thermostat to the desired temperature and run the heater for testing.

Electric water heaters are usually equipped with two thermostats: lower and upper ones. The upper one has a high limit, which is non-adjustable, and when it trips, it must you must reset it manually. If the hot water inside the heater increases to an extremely high temperature, the high limit switch is triggered, it interrupts the heating, so it requires manual reset.

Problems when the thermostat is not working properly

  • If the temperature is set too low, there will be not enough or no hot water inside the tank.
  • If the temperature is set too high, the outgoing water is too hot.
  • Overheated water and continuous operation are the results of an improperly installed thermostat - it is not in contact with the tank.

When selecting the location for the electric water heater, it is crucial to provide adequate clearance between the thermostat and surrounding elements so the thermostat can easily be used for temperature change, replaced if broken, and cleaned as part of regular maintenance.

Words of caution

Do not perform any work on the thermostat or water heater with the power ON. Always make sure that the breaker is in the OFF position. It is recommended to contact a professional for the proper thermostat replacement.


As said before, this guide is for homeowners who are capable of doing DIY home projects. The guide provides some useful tips that will help you learn how to replace an electric water heater thermostat, identify and solve problems that can affect the proper heating.

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