How to Test the Water Heater Thermostat

(Last Updated On: April 13, 2020)

Sometimes on cold days you may face some problems with hot water in your taps. You may see that there is no hot water or maybe there might be hot water initially but suddenly it becomes cold again.

There can be two causes for this problem. If there is no hot water at all, then it likely means that the upper thermostat has gone bad. If you’re getting hot water but it’s not hot enough, then it likely means that the lower thermostat has gone bad.

A thermostat is necessary for maintaining the heat flow at an optimal rate in your water heater. If it goes bad in cold days, then your life may become a survival story and you’ll be in an internal battle with your mind about whether you shower or not. Or, if you have a friendly neighbor, maybe you can go to his/her house to bath. To avoid this, from time to time, you should test your water heater thermostat.

How does a water heater thermostat work?

A water heater generally has two thermostats. One is in the upper level and the other on the lower level. This thermostats control the heating element. It activates the heating element to heat the water when it gets cool and it stops them from heating the water once it has reached the desired temperature. A water heater thermostat controls the temperature of the water and keeps it in your desired temperature. It does this by controlling the heating element’s behavior.

What causes a thermostat to lose power?

There’s no fixed reason for a thermostat to lose power. But in most cases it may have shorted out or there was some kind of resistance in its contact.

How much does it cost to replace a water heater thermostat?

A water heater thermostat can be changed if it goes bad. But it might cost you quite a bit. Usually the average cost of replacing or fixing your water heater thermostat ranges from $150 to $200. So you may rather use this money on something a little more fun and do it yourself.

How do I test my thermostat with a multimeter?

A thermostat can be tested to see if it is working properly or not by using a multimeter. You can find our recommended multimeters here. By looking at the reading of the multimeter you can decide whether your water heater thermostat is working properly. Ensure your multimeter is set to RX1. If yes, then start following the steps below:

Steps to test water heater thermostat

A water heater has two different thermostats on it. One thermostat is on the upper part of the heater and the other one is in the lower part of the heater. Below, you will learn how to test both of them and make sure that they are working properly or not. Before starting the steps make sure you have the following tools – A Philips screwdriver, a multimeter, safety gloves and safety shoes.

Switch off the water heater

First thing you should always do while testing any kind of electrical appliance is to switch the power off. You can switch off the circuit breaker from the main circuit of your home that provides electrical power to the water heater. This will keep you safe from getting an electric shock from the heater.

Remove the access panels

Now you will need to remove the access panels of your water heater. The thermostat and the heating element are below it. So safely remove the access panels from your water heater, make sure you’re wearing safety gloves for protection.

Remove the insulation and safety cover

Now, you will find insulation below the access panels. This insulation reduces the risk of current touching any conducting part of the heater keeping you safe from any hazard. Safely remove this insulation first gently so that any wire doesn’t accidentally get pulled off. Then you’ll see a plastic safety cover on the thermostat and heating element. Remove this safety cover to start testing your water heater thermostat.

Test the upper water heater thermostat

  • Use a Philips screwdriver to turn the temperature of the upper thermostat to maximum. Turn it to the highest temperature you can see in the thermostat.
  • Do the opposite for the lower thermostat now. Use the screwdriver to reduce the temperature of the lower thermostat and take it to the minimum possible value.
  • Now turn on the power of the water heater. Make sure you’re wearing all the necessary safety equipment, such as rubber gloves and shoes.
  • Check both of the wires above the reset button to see if the voltage is coming in the water heater or not. Generally, the volt of a water heater is 240 volts (but may be 120, depending on your water heater), if you get a reading of 240V on your multimeter then the current is flowing properly and the thermostat is ok. If you get any other reading then the thermostat may be faulty.
  • Now check if the heating element is getting any current or not. To check it, place the probes of the multimeter on the screws touching the heating element. If you get a reading of the power then the thermostat is good, if not then your thermostat needs to be replaced. Before you do that, first check if the lower thermostat is ok or not.

Test the lower water heater thermostat

Now if your upper thermostat is good, you should continue the testing process and check if the lower thermostat is good or not.

  • Use the screwdriver to change the temperature of the upper thermostat. Decrease the temperature of the upper thermostat to lowest setting.
  • You must hear a click off sound while doing this. If you don’t hear it then wait and let the water inside the tank to get heated up more. Once done then try again.
  • Again using the Philips screwdriver to turn the dial of the lower thermostat’s temperature and increase it. Change the temperature of the lower thermostat to the highest possible temperature.
  • Now check the voltage of the lower element. If you get a power reading, start to reduce the temperature of the lower thermostat. Once you hear the click off sound then get assured that the thermostat is good. But if you don’t have power at the element, then go to the next step.
  • Now test the lower thermostat for power. Place one probe on the upper contact screw of the lower thermostat and other probe on the tank’s surface. If you get a reading of 120V on the multimeter, then your upper thermostat is ok and it’s sending power to the lower one. If you don’t get a reading, then you may have a faulty upper thermostat. If you are getting power, then go to the next step.
  • Now place one probe on the lower contact screw of the lower thermostat and the other probe on the surface of the tank. If you get a reading of 120V then your lower thermostat is working properly. If you don’t get any reading, then the thermostat has gone bad and needs to be replaced.

Replace the safety cover and insulation

Now once you have done testing the water heater thermostat, put the safety cover back on it again. After putting the safety cover on, replace the insulation. Make sure you’re still wearing safety gloves.

Replace the access panels

Now, after insulating the thermostat properly, put the access panels back on it again. Make sure it fits properly and doesn’t have any open space. Current leakage could be a safety hazard to anyone touching the water heater accidently.

Switch on the current of the water heater

Now go back to the main current circuit and switch on the circuit breaker that provides current to the water heater and you’re all set.

Tankless Reviews was created with the goal of helping people to understand the benefits and practical knowledge related to tankless water heaters. After purchasing my very first tankless heater years back, I realised that other people needed to hear about the incredible money-saving ability of this household item, and wanted to share my lessons with you!