If hot water is scarce at your house, make sure the water heater’s thermostat is set correctly. If it is, then you might have a problem. Let me show you — in just 4 steps — how to replace a water heater thermostat that has gone bad.

Table of Contents

Should You Replace the Water Heater Thermostat?

Firstly, you need to determine if you need a thermostat replacement. Then, go ahead and drain the water heater tank if you suspect it is filled with sediment. If you have no hot water, check the unit for power.

If neither of these measures solves the problem, you might need to replace the thermostat or the heating elements. To confirm the problem, remove the thermostat and the heating element and bring them to a plumbing supply house or appliance repair shop for testing.

Follow the steps below if you need to know how to replace a water heater thermostat. If it’s the heating element, go here for instructions.

Leaking water heater - drain water (flush tank) — Start this project by draining your water heater tank. If you have too much water for a bucket, connect a garden hose to the drain spigot and place the other end in a floor drain.

How to Replace a Water Heater Thermostat

Electric water heaters have 2 thermostats and 2 heating elements.

To find out which pair is defective, turn on a hot water faucet. If the water gets warm but not hot, the upper thermostat and element will need to be replaced. However, if the water is hot for a short while, then goes cold, replace the lower element and thermostat.

This job will take about 2-3 hours, depending on your skill level. More so, you should know how to make electrical connections safely to do this as a DIY job. You’ll also need a screwdriver and a voltage tester.

how to replace a water heater thermostat voltage tester by Fluke — You’ll need a voltage tester to do this job. The pen-style non-contact tester in this photo is made by Fluke. It’s safe, easy to use, and affordable.

1. Check the Power

Shut off the power. Go to the main electric panel and turn off the circuit for the water heater. TIP: If you haven’t labelled your circuit breakers, the circuit for an electric water heater is most likely on a 30-amp breaker. Shut off all the 30-amp breakers until you find the water heater switch. Then label it for future reference.
Remove the screws from the water heater access panel and lift off the panel.
Remove any insulation in the panel that is in your way.
Check for voltage using a voltage tester.

how to replace a water heater thermostat - 1 turn off power at breaker box — Your first step should always be to turn off the electric water heater’s power at the electrical panel (also called a breaker box). It should be labeled for your water heater. If not, turn off all of the 30-amp breakers.

2. Remove the Thermostat

Before disconnecting all the thermostat wires, label them. This will help you later when you have to reconnect the wiring (the correct wire to the correct terminal).
Disconnect the wires from the old thermostat.
Remove the mounting clip and lift out the thermostat. TIP: Always replace an old thermostat with a new thermostat of the same model.

how to replace a water heater thermostat - 2 remove insulation to check thermostat — Move aside the insulation so you can work on the thermostat and remove it from the electric water heater’s service panel.

3. Install the New Thermostat

To jook up the new thermostat, attach the mounting clip.
Reconnect the wires to the terminals using your labels as a guide (and that’s why you want to label the wires in step 2 above).

install new part with mounting clip or bracket — Your new thermostat will come with a mounting clip or bracket to make sure it stays in place.

4. Reset the Power

Read the water heater manufacturer’s instructions for the recommended temperature setting (it’s probably 120 degrees but always under 140 degrees).
Make sure the tank is full of water.
Turn the power back on at the circuit breaker.
Press the red reset button on the thermostat.
Replace any insulation you removed and reinstall the access panel.

reset the red button — You can’t miss the thermostat’s reset button. It’s the only button and it’s red!

Caution: Danger, High Voltage!

Electric water heaters use a 240-volt current. That’s twice the voltage found in standard receptacles. So, be sure to remove the fuse or shut off the breaker at the service panel.

Use your voltage meter to test any wires for electricity before starting any work. Keep in mind, a 240-volt circuit will probably have 2 fuses or a tandem circuit breaker.

Final Thoughts

In conclusion, learning how to replace an electric water heater thermostat is easy. The scariest thing to get past is working with electricity. But as long as you turn off the power at the breaker box and drain the tank of water, you’ll be perfectly safe.

Call 1-Tom-Plumber

Overall, don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need help servicing or replacing parts on your water heater.

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

How To Replace A Water Heater Thermostat (Danger! High Voltage!)

Should You Replace the Water Heater Thermostat?