An electric water heater thermostat tells the heating elements when to heat up. Most electric hot water tanks have two elements and two thermostats. The elements do not heat up at the same time. The top element heats the water first and then the bottom element kicks in.
The upper thermostat acts as a coordinator between the two elements. When the water in the top part to the tank is hot enough, it lets the lower thermostat go into action. When the lower thermostat senses the water is too cool it turns on the lower element. This happens only after the upper element has finished heating.
You need to do some testing to determine which element or thermostat is bad. Go to the article Hot Water Heater Element Testing for information on how to test the elements and thermostats. Have you already determined that one or both of your thermostats is bad? Then you are at the right place.
There is another reason you could be here. To adjust the temperature of the water you need to get to the thermostats. These thermostats are a little harder to adjust than your furnace is. There are a couple of things you need to do to expose them.
The upper thermostat is around $20 to $25 and the lower one is $10 to $15. You will probably pay around $100 in labor to get them
Replacing an electric water heater thermostat is not that hard of a job. You are dealing with some serious electricity and that adds a safety factor.
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Try the reset buttons before you replace the thermostats. Each thermostat has one.
Do not work on the wiring for an electric hot water heater with the power on. Make sure the breaker is shut off and taped or locked in the off position. The current in a hot water tank can kill you. Replacing the wrong thermostat may still leave you without hot water or not enough hot water.
The 'Next' section discusses 'Cutting Power to a Water Heater'. Check the 'Home Repair Topics Menu' at the top of the page, if this is not your problem.