How To Replace The Upper And Lower Thermostat In Your Electric Water Heater

Posted on: 20 May 2016

An electric water heater is set to reach an ideal temperature that will provide you with hot water without risking scalding. The unit knows when that temperature is reached thanks to a thermostat that operates similarly to a furnace thermostat: once the warm temperature is reached, the unit stops heating.

Unlike a furnace, a water heater has two thermostats with one in the upper half and one in the lower half of the unit. The thermostats ensure that the water is being heated throughout the tank rather than only in one half, which would mix with the colder half and come out lukewarm.

Replacing a water heater thermostat isn't hard once you're sure that is the cause of your heating issue and you've purchased the correct thermostat replacements from a plumbing supply store. And it doesn't really matter whether it's the upper or lower thermostat to blame since both uninstall and replace in the same way.

What You Need:

  • Screwdriver
  • Electrical tape
  • New upper or lower thermostat

Step 1: Locate and Access the Thermostat

Turn off the electricity to the unit using the shut-off switch or by flipping the breaker in the circuit breaker.

Locate the access panel doors for the thermostats, which are two identically sized doors that are vertically across from one another. Use a screwdriver to remove the fasteners holding the panel door in place over the upper or lower thermostat that you plan to replace. Remove the door and set the door and screws aside for safekeeping.

You will now see an insulation flap covering the hole. Lift the bottom of that flap until the insulation piece is fully opened and pressed up against the exterior wall of the water heater. Secure the insulation in place using a strip of electrical tape.

Use the edge of your screwdriver to pry up the plastic cover over the upper or lower thermostat. Set the plastic cover aside with the other parts.

Step 2: Unhook the Old Thermostat and Install the New Thermostat

Pay attention to how the wires are attached to the thermostat. Use your screwdriver to loosen the mounting screws holding each wire in place and allow the wires to dangle inside the water heater.

Locate the mounting tabs on each side of the thermostat. Slide the end of your screwdriver into the tabs and pop the tabs out of their slots. Pull the old thermostat free of the water heater.

Insert the new thermostat by sliding its tabs into the slots and pressing backwards to snap into place. Hook the appropriate wires up to the terminals on the new thermostat. Tighten the mounting screws to secure the wires.

Step 3: Put the Water Heater Back Together

Snap the plastic cover back into place over the thermostat. Remove the tape holding the insulation and press the insulation back into place over the plastic cover. Place the access panel door over the upper or lower thermostat and secure into place with its screws.

Restore the electricity to the unit at the switch or breaker. Conduct a test run to see if your water is adequately heating. If you still have lukewarm water, call in a plumber for help.

For more information, contact Day's Plumbing Supply Inc or a similar company.


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After we moved into a new home, I could tell that the plumbing system was having problems. Our drains never really drained quickly, and there was always the faint smell of sewage in the background. I knew that I wanted to fix the problem, but I didn't really know where to start. However, I knew that I didn't want to take care of the problem, so I called in the experts. My friend, who worked as a plumber, came out and worked hard to diagnose the issues. After we got things fixed, our house smelled and functioned better. This blog is all about diagnosing plumbing problems.


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