How To Test The Water Heater Thermostat in 10 Simple Steps

How To Test The Water Heater Thermostat

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If your electric water heater is not working properly, the thermostat could be the problem. However, when you open the unit, you will see two thermostats, and you have to determine which one is not working.

Below we discuss how to test the water heater thermostat in ten simple steps.

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Steps on How to Test a Water Heater Thermostat

1. How The Thermostat Works

To understand how to test the water heater thermostat, you have to know how it works.

If your water heater is not working, then the thermostat is the culprit or at least part of the underlying problem. Replacing the thermostat may be all you need to have your heater up and running again.

Also Read: How Does A Tankless Water Heater Work?

Modern heaters come with two thermostats and two heating elements. There is an upper thermostat that is often large and the lower thermostat.

It is rare for both thermostats to fail at the same time, so you need to check which one isn’t working. Mostly, when the upper thermostat fails, the heater will not produce hot water.

If the lower thermostat is the problem, the upper one will continue heating water in the top part of the tank. This will mean that the hot water will quickly run out or you only get lukewarm water.

Below are steps on how to test the water heater thermostat.

2. Turn Off The Power Supply.

Go to your circuit board and turn off the circuit breaker. Check for the breaker labelled Water Heater inside the panel box.

Remove external access covers.

You will need a flathead screwdriver or a nut driver to complete this step. Use any of these to remove the lower and upper thermostat access panels.

Be careful to fold back the insulation used over the thermostat. You can use tape to hold the insulation in place and out of your way.

At this point, you should be able to see the interior plastic used to cover the thermostat. Remove this as well.

Confirm that there is no power getting into the water heater

It is easy to complete this step if you have a power stick. Touch the top to bottom of the multimeter connections at the same time with your power stick.

If the reading is zero, you are sure that the power supply is off. If not, some power is getting to the heater, and the last thing you want at this point is some electric shocks hitting you when you are trying to disconnect any part of the heater.

3. Check If The High Limit Reset Button Is Working Properly.

This reset button may trip if the heating element is not working or if the thermostat calibration is out. The thermostat fuse may also be closed.

4. Disconnect The Wiring

Use a screwdriver to disconnect the wiring going to each of the thermostat terminals.

For reference’s sake, you can use a camera or your phone to take a picture of how the wiring looks before disconnecting. This way, you will know which wire goes where when reassembling your unit.

5. Use A Multimeter To Check The Thermostat.

An analogue multimeter is the best tool to check the thermostat. Set it at the lowest resistance and calibrate it by bringing the probes together and ensuring that the needle is at zero.

You may also use a digital multimeter and also set it at the lowest resistance, which is usually 200 ohms.

Whichever multimeter you have, take the black probe and place it over the left side terminal and the red one on the terminal on the other side.

If there is continuity of power, the meter reading will be close to zero. If this is not the case, then it means that the thermostat is not working and you need to get a replacement.

Repeat this process on the right side and also on the lower thermostat. Once you are done testing, you can reconnect the wiring and close up the panels or take the necessary steps to get some new thermostats.

It is always advisable to replace both the upper and lower thermostats at the same time, especially if you need some extremely hot water. Fortunately, thermostats are quite affordable, so you do not have to spend much on a set.

Replacing The Thermostat

Aside from knowing how to test the water heater thermostat, you also need to know how to replace it. Below are the steps to take when replacing.

Remove the thermostat

At this point, the thermostat should be exposed, so the first step is to remove it from its casing. Use a screwdriver and a finger to bring it to the surface and remove it gently.

Be gentle not to break the bracket that holds the thermostat. If you break the bracket, you may be forced to replace the whole water heater.

Insert New Thermostat

Place the new thermostat where you removed the defective one. The bracket should hold it tight so you can have your hands free to reconnect the wires.

Reconnect all wires properly and ensure they are all firm. This is where the photo you took before disconnecting the wiring comes in handy.

Ensure that the thermostat rests firmly on the water heater; otherwise, it may not function as efficiently.

Once the thermostat is in place, set it to the desired temperature. Use a flathead screwdriver to adjust the thermostat.

A maximum temperature of 120 degrees is recommended. Higher temperatures are a scalding hazard, especially if you have children and older people in your household.

Also Read: 5 Easy To Spot Signs of a Busted Water Heater

Reattach Power Supply & turn the power on

Now that the thermostat is set, put the insulation back in place, replace the protective cover and reattach the external access panels.

Go back to your electrical box and turn the power back on. Once the power is back, allow some time for the tank to recover.

Ideally, you should let the heater rest for about an hour before using it as this allows adequate time for it to recover.

However, if you are in a hurry, you should be able to get some hot water within 14 minutes.

Don’t forget to keep an eye on your water heaters performance often and act quickly whenever something is amiss.

If you the performance doesn’t improve even after replacing the thermostat, you may need to call a professional to check and diagnose your heater.


A thermostat is an integral part of your electric water heater. When it is faulty, you may have to endure cold water in your taps before it is fixed.

Fortunately, thermostats are inexpensive, and they are also easy to fix. The steps above will guide you on what to do to ensure that your water heater unit is working in no time at all.

Click here to search for thermostats on Amazon.