How to Change a Hot Water Tank Thermostat

Most of the electric hot water tank heaters which are manufactured in this modern time make use of dual element system. Only the older units and a few new models use a single element. For each of the elements, there is a unit which requires a corresponding thermostat, this means that two-element devices have two thermostats and the models of a single element have just one thermostat. When you’re replacing a thermostat, it is advisable to replace the upper and lower thermostats.

Testing the thermostats in a two-element water heater system

Because most of the electric heaters use both the upper and a lower element, the following process below is for these systems. To test, you will need both a multimeter and a screwdriver. You can buy a cheap multimeter online or at a local store.

Testing the upper thermostat:

Turn the power of the water heater off. Then the access panel to the elements must be removed, the underlying insulation too must be removed with it.
The thermostat needs to be set above the maximum, so you may use a screwdriver to set this above the maximum setting.
The lower thermostat has to be set to the lowest setting. After that, you should turn the power to the heater back on.
Ensure there is a supply of current to the water heater. Do this by checking the reset button, it must read 240 volts.
Then you may use the multimeter to check the power on the screws of the upper element terminal. If there is no power supply, this thermostat is damaged and must be replaced. If it still have power, then you may proceed to check the lower thermostat.

The Lower thermostat test:

To test the lower thermostat, you must first set the upper thermostat to the lowest setting.
Then the lower thermostat should be set to the highest setting.
Please ensure voltage reaches the lower element. When the meter shows there is a supply of energy to the element, then you must wait a few minutes, this is to allow the water to warm up.
Reduce the temperature of the thermostat and then wait for an audible click to indicate that the thermostat is working properly.
If after testing, you discover any issue which warrants changing the thermostat, then you may go ahead with the following.

Replace the electric heater thermostat

To replace the electric thermostat, always turn off the power or turn off the power switch. To change the thermostats, you must remove the access panel and the safety cover (this applies to the top and bottom access panels of the dual-element units). For safety reasons, use a voltmeter to make sure the unit is turned off. You can make a simple diagram showing how the cables are connected. Then remove the wires from the thermostat

The thermostats are placed in a special holder that holds them firmly against the tank so that the thermostat can detect the internal temperature of the water. Gently lift one side of the bracket by turning upward that side of the thermostat to prevent that bracket from coming back into place. Repeat this also for the other side. Repeat the process for the lower thermostat on the dual-element models.

If the bracket became damaged as the thermostat was being removed, a replacement bracket can be obtained. The old bracket can be lifted to remove it, and a new one may be flatly placed against the tank and pushed down until it snaps into place.
You must replace each of the thermostats by sliding it into the holding bracket evenly until it snaps into place. Then replace the wiring just as it was removed (as shown in the diagram you have drawn). Replace the safety covers you removed as well as the access panels. You may now restore power and run the water heater for about an hour to check if the water is hot.