Water Heater Thermostat

If your looking for water heater thermostat information you can find it all here. How to test or replace a thermostat. How to check the limit switch, adjust the temperature, buyers guide and more.




How a thermostat works

Water heater thermostats are actually very simple devices. They
operate off of a bi metal switch located in the back of the thermostat.
When the bi medal disk reaches a certain temperature it will pop in or out which ever the case may be and connect or disconnect the power supply to the heating element. This bi metal disk is what you hear clicking when the temperature is turned up or down.



Thermostat and limit switch

water heater thermostat

The thermostats in this pic are for a duel element 240 volt storage water heater.

The thermostat on the left is the upper or primary thermostat.

The thermostat on the right is the lower or secondary thermostat.


water heater limit switch

The upper thermostat is mounted onto a limit switch.
I have separated the limit switch and thermostat so you can see each one separately.

This limit switch (top of pic) has a red reset button.


switch relay

As you can see this thermostat is very simple.
Power enters the thermostat on the top left terminal. When the thermostat calls for heat power is sent to the lower left terminal which energizes the upper element

When the thermostat is satisfied power is then sent to the upper right terminal and is transferred to the lower thermostat.


lower t-stat

This is the lower thermostat.
Power is sent to the top terminal from the upper thermostat.

If the thermostat calls for heat power will be transferred to the bottom terminal which will energize the lower element.



single element water heater thermostat

The thermostat on the right is designed for a single element water heater.

The thermostat on the left is designed for a duel element water heater.

As you can see the single element thermostat only has two terminals.
Power comes into the top terminal from the upper thermostat.
When this thermostat calls for heat power is transferred to the lower terminal which energizes the lower element.


Water heater thermostat buyers guide

If your shopping for a water heater thermostat the two things you'll
need to know are the number of elements in the water heater and the
voltage of the water heater ( check the label on your water heater).

If the label is missing from your water heater you can find the
voltage written on the end of the water heater element.

The upper thermostat and limit switch are always sold together.

There are several brands of residential tank type electric water heaters. You do not have to buy a brand specify thermostat.

If you must replace a thermostat its always a good idea to replace both thermostats at the same time.



Related links

Test a thermostat
How to check a thermostat with the power off. Thermostats can be tested with the power on or off. You can check the voltage at the element to see if the thermostat is working if your comfortable working with the power on.

Replace a thermostat
Replacing a thermostat is easy with this step by step guide.
No special tools required.

Water heater reset button
What to do if the reset button pops out. How to reset your water heater limit switch.

Water heater temperature
How to adjust the temperature on a thermostat. What temperature should
your water heater be.

How to use a multimeter
How to read a multimeter to check continuity and voltage with an analog multimeter.


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