How to Replace a Water Heater Thermostat

Updated
Categories Water Heating
Need to replace your water heater’s thermostat? Here's how.

Is the water coming from your hot faucet suddenly too hot? Did you try adjusting the temperature but nothing changed? Then it’s probably time to replace the water heater’s thermostat.

Depending on your water heater, replacing the thermostat shouldn’t be a big deal. We’re here to walk you through the how to’s and tell you a little about what to look out for.


How to Replace a Water Heater Thermostat

Replacing a thermostat yourself is fairly easy, but the procedure differs a bit depending on how many heating elements your tank has.

Most of today’s electric water heaters include two heating elements. Smaller units or older models usually only have one.

For each of those heating elements, your tank has a matching thermostat. If your unit has a dual element system, it has, and requires two comparable thermostats. The single element system requires one.

Because most water heaters have a dual element system, we’ll focus on that here.

A good idea

Even if there’s only one faulty thermostat, it’s recommended to replace both. The upper thermostat supplies power to the lower, so replacing both saves time.

Here’s what you need to replace the thermostat:

  • A multimeter or voltmeter.
  • Screwdriver.
  • Flat blade screwdriver.
  • Different colored tapes or bandages.
  • A new thermostat, identical to the old one wherever possible.

1. Turn the Power Off

Start by turning the power to the water heater off. Do this at the breaker box by turning the breaker to the “Off” position.

2. Check Upper and Lower Thermostats

Before you replace the thermostats, it’s essential to check them first. For this, you’ll need the multimeter and a screwdriver.

Start by removing the access panels and the insulation sitting before the elements. Then, with the screwdriver, turn the upper thermostat to the highest setting. Then turn the lower thermostat to the lowest setting.

Turn the power to the water heater back on. Use your multimeter or voltmeter to check if a voltage is coming through. Place it on the two wires just above the reset button — here it should read 240 volts.

Next, place the multimeter on the terminal screws to the upper element. If there’s no power, the thermostat is broken and you can proceed to replace it. If there is power, check the lower thermostat.

Take the same steps as above. But now turn the lower thermostat to the highest setting and the upper thermostat to the lowest. Then check for voltage.

If there’s voltage, you can just replace the upper thermostat. However, if there are no signs of power, replace them both.

3. Turn the Power off Again

After you’ve established that one or both thermostats need replacing, turn the power to the unit off again. Do not proceed with the water heater still connected. Use the voltmeter or multimeter to check for any voltage.

4. Remove Bracket

The thermostats are secured by specialized brackets that firmly keep them in close contact with the tank. This is so they can sense the water temperature.

Use the shaft of the screwdriver and gently but firmly pry the bracket out one side at a time. Pry one side of the bracket while you slowly twist the thermostat upwards. This will prevent the bracket from locking.

Don’t worry about the bracket if you accidentally break it. These are easy to replace as well.

5. Disconnect the Wires

Disconnect the wires one by one. When you disconnect one wire, place a small piece of some colored tape or band-aid on the wire and its terminal.

Use a different color for each wire and terminal set. This will help you replace them in the right spot once you’re finished.

6. Remove the Thermostat

This is probably the hardest part, and you should be very careful. Start by loosening the screw terminals holding the thermostat in place. Remove each wire from its terminal.

Looking at the thermostat, you’ll see that it sits in retaining clips. Gently remove it from the clips, and place it to the side.

Watch out

Be careful — you might not be able to repair or replace the clips should they break or bend. In some cases, damaged retaining clips will require you to purchase a new water heater.

7. Install New Thermostat

Remember that the new thermostat must be identical to the one it replaced. If not, it might not work well, or at all.

Grab your new thermostat and place it into the retaining clips. Place it so it rests firmly against the tank wall.

Reconnect the circuit wires to their correct screw terminal. Be sure that they’re matching the original wiring. This is where the color-coded tape comes in handy — remember where each color should go and remove the tape.

Use the screwdriver to tighten the screw terminals — make sure they’re tight.

8. Set the Temperature

Once the thermostat is in place, set the temperature. Use the flat-bladed screwdriver and gently turn the thermostat to your desired temperature.

Remember

The recommended temperature to set a water heater to is 120 degrees Fahrenheit. This is ideal for both efficiency and safety reasons (1).

9. Replace Insulation and Cover

You’re almost done! Now replace the insulation so that it covers the thermostat and electrical components. Place the compartment cover back on and secure with the screws.

Turn the power back on at the breaker box and allow the unit at least two hours to heat up. After two hours, you can test the water temperature by turning on the faucet.

Are All Thermostats the Same?

Electric water heater thermostats are relatively simple devices. They work using a bi-metal switch sitting at the back of the thermostat, which senses the temperature of the tank.

When the water inside the tank reaches the set temperature, the bi-metal switch pops in or out. This either connects or disconnects the unit to prevent the water from overheating. Usually, when you adjust the temperature, you hear a click, this is the metal switch adjusting the temperature.

Although it’s recommended to find an identical replacement, it might not always be possible. If you can’t find a thermostat identical to the last one, check how many elements are in your unit and the voltage they use before looking for a compatible one.

But if there’s no label indicating the voltage, refer to your owner’s manual. If that fails, most residential water heaters are 240 volts.

Another reason why you should always try to replace the former thermostat with an identical one is the difference between dual and single.

Thermostats used on a single-element water heater have only two screws on the right side. Thermostats for a dual element tank, on the other hand, have three screws on the right side.

A dual element thermostat may still work on a single-element tank. However, a single-element thermostat cannot work on a dual tank.

Gas Water Heater Thermostats

If you have a gas water heater, replacing the thermostat isn’t as straightforward. For starters, the thermostat on a gas unit is integrated into the gas control valve. So, if the thermostat isn’t working properly, you’d have to replace the whole gas valve.

Although you might be able to do it if you have experience, we highly recommend you don’t. Changing the gas control valve includes dealing with multiple gas connections. If something isn’t connected correctly, the outcome could be dire.

Hence, we recommend contacting a heating contractor or your local plumber. Additionally, in some cases, a faulty gas valve is so expensive that you can warrant it for a new unit. This is especially the case if the unit is near the end of its warranty or severely damaged.

Not a Faulty Thermostat?

If the water is suddenly overheating, and you know it’s not the thermostat, check your water. One of the most common causes of scalding hot water is water with high mineral content.

If the area you live in has hard inlet water, this is definitely something to check. Hard water is groundwater which is high in minerals such as magnesium and calcium. These minerals like to collect around the heating elements where they eventually cause corrosion and a crust.

In turn, this inhibits the heating elements from working properly. Over time, they begin to work harder and eventually overheat and burn out (2). This will cause the water inside the tank to overheat as well.

Luckily, you can fix this by replacing the heating elements and regularly flushing out your unit.


Get It Done

Replacing a water heater thermostat is relatively easy if you have an electric unit. Simply switch off the power, disconnect the wires and carefully remove the thermostat, then replace and connect. However, if you have a gas unit, call a professional — gas is dangerous to work with so there’s no room for error.

If you’re replacing your electric thermostat, remember to buy an identical one. But, if you have hard inlet water, make sure to check the heating elements. They might be the source of the trouble and not the thermostats.

Are you willing to try your hand at replacing your thermostat? Let us know how it goes! Or if you have further questions or comments, leave them for us below.

Headshot of peter

About the Author

Peter Gray

Peter has been a homeowner for 35+ years and has always done his own repair and improvement tasks. As a retired plumber, Peter now spends his time teaching others how they can fix leaks, replace faucets, and make home improvements on a budget.
Best Water Heater Blankets of 20205 Best Water Heater Blankets You Can Buy (2020 Reviews)
How the Best Under Sink Water Heaters Can Make Your Home Energy EfficientBest Under Sink Water Heaters of 2020
On-The-Go Hot Water: The Best Portable Tankless Water HeatersBest Portable Tankless Water Heaters of 2020
4 Best Condensing Water Heaters (2020 Reviews)The Best Condensing Water Heaters (Go Environment-Friendly)
Best Hot Water Recirculation Pumps of 20205 Best Hot Water Recirculation Pumps (2020 Reviews)
The Best Water Heater Flushing Kits (Never Lose Hot Water Again)Best Tankless Water Heater Flush Kits of 2020

Leave a Comment