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Water heater thermostats are heat sensitive devices.

They control electrical current to either a water heater element or another thermostat.
Thermostats are components of devices when a certain temperature is to me maintained.
Such items include: water heaters, refrigerators, freezers, all heating and air units just to name a few.

How many Thermostats in a water heater?

In a single element point of use water heater you have 1 thermostat. This thermostat contains the high temperature limit switch (ECO).In two element residential or light duty commercial water heaters you will have 2 thermostats, the upper thermostat and lower thermostat.The upper thermostat will contains the temperature high limit switch (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

In large commercial water heaters you can have 2 or 3 thermostats each controlling multiple elements.

In gas fired water heaters the thermostat is contained in the gas valve.

Water heater natural gas valve with thermostat probe

AO Smith 9008218005 natural gas valve showing thermostat probe

Sequence of operation of water heater thermostats:

For a single element residential or commercial water heater:
Power is applied from your electrical panel through the high limit switch (ECO) and thermostat to one side of the water heater element.
When the water temperature drops below the setting of the thermostat, the thermostat’s contacts close.
Power is now being supplied to both sides of the water heater element.
The element will continue to heat the water until the thermostat is satisfied and the contacts open.
With the contacts open, the electrical current is discontinued.

For a dual element residential or commercial water heater:
Power is applied from your electrical panel through the high limit switch (ECO) and upper thermostat to one side of the water heater’s upper element.
When the water temperature drops below the setting on the thermostat, the thermostat’s contacts close.
Power is now being supplied to both sides of the water heater element.
The element will continue to heat the water until the thermostat is satisfied and the contacts open.

Once the upper thermostat is satisfied, power will be diverted to the lower thermostat.
The lower thermostat will supply power to the lower water heater element until the thermostat is satisfied.
The lower thermostat’s contacts open removing power from the element.

Interesting note: the upper thermostat is the primary thermostat due to the fact that when there is a call for hot water, it flows from the top of the tank!
In commercial electric water heaters, one thermostat may control 2 or 3 water heater elements.
In gas fired water heaters, the gas valve normally contains the thermostat.
The thermostat will have a probe that is immersed into the water heater tank thru a port located near the bottom of the water heater.

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!”