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You may have a thermostat problem If your water heater is not maintaining the water temperature you have set!

In this article we will cover how to check a water heater thermostat for proper operation.

We will cover both single element and dual element water heaters whether residential or commercial.

In our last blog, https://blog.wallingfordsales.com/water-heater-thermostats/,  we discussed that a thermostat is a heat sensing devise that controls electrical current either to another thermostat or water heater element.
As pictured below, we stated that in a dual element water heater that the upper thermostat contains the temperature high limit switch, the ECO.

AO Smith 9001954015 Upper Thermostat with temperature high limit switch (ECO) and cover

AO Smith 9001954015 Upper Thermostat with temperature high limit switch (ECO) and cover

Before checking our thermostat, we must be sure our water heater elements are good.
If we have an open or grounded element, we will get a false thermostat reading.
Please go to my blog https://blog.wallingfordsales.com/water-heater-element-troubleshooting on how to troubleshoot water heater elements.

For this study we will assume that your heater is supplied with 240-volts.

Steps for checking thermostats.

Step 1. Check for power to your water heater.

Place the leads from your multi-meter across the terminals at the top of the thermostat pictured above. Your meter should read 240 volts. If not check your electrical panel.

Step 2. check for power through the temperature high limit switch (ECO).

Place your leads across the 2nd set of terminals from the top and you should get 240 volts. A 240 volt reading means you are getting power thru your temperature high limit switch. If you get no reading replace that thermostat.

Step 3. When checking the thermostat in a single element water heater or the upper thermostat in a dual element water heater the process is the same.

Turn the upper thermostat to it’s highest temperature, and if checking a dual element heater the lower thermostat to it’s lowest setting. This will force the upper thermostat to call for heat and force the lower thermostat to shut-off. Now find the 4th set down of terminals on our pictured thermostat and place your meter lead on the left terminal and the other lead to the right side terminal of the water heater element. You should read 240 volts. Now, leaving the lead to the right side of the element in place, move the other lead to the left hand single thermostat terminal. You should read 240 volts. This shows that the internal thermostat switch is working.

Step 4. When checking the lower thermostat in a dual element heater, turn the lower thermostat to it’s highest temperature and the upper thermostat to it’s lowest temperature.

This will force the lower thermostat to call for heat and the upper thermostat to shut-off.
Place the lead of your multi-meter on the incoming power side of the thermostat terminal of the lower element and the other lead on the opposite water heater element terminal. You should read 240 volts. If not, then you need to replace the lower thermostat.

 Warning: Always make sure that the water heater tank is full of water before applying power!

Doug Wallingford
www.wallingfordsales.com
www.waterheaterstore.co

“Keeping you in hot water…so you stay out of hot water!”