Electric water heaters will have some problems from time to time. You can expect some thermostat related problems after a few years of everyday use. Thermostats are the regulators that will control the temperature of the water. Some thermostats can be used to set hot, hotter, hottest temperatures. Some thermostats allow you to set an exact temperature using its digital interface. Regardless of the nature of the interface and the type of electric water heater you have, there will be heating problems. The water heater may not heat the water at all, it may heat mildly or it may heat too much.
Remember a few things before you try to troubleshoot a thermostat. When you check different components of an electric water heater, you do so after turning off the power. You cannot inspect a thermostat with the power turned off. Hence, make sure you don’t touch any exposed element or powered component of the electric water heater. You would get a shock. Some shocks can be fatal.
Whenever there are heating problems, they could be due to one of the many components including heating elements or it could be due to the thermostat. You should check the voltage of the heating elements. You can do this using a test lead connected to each of the wire terminals. Of course, you should check one terminal at a time. When the water is hot inside the tank, there must not be any voltage. Wait for the water to get heated up if you have just turned on the power. If after the water is heated the elements remain hot then you should replace them. You may have to replace one or both the thermostats depending on your observation.
What to Do
You should check the lower thermostat when the tank inside has hot water. The reading should be 240V. If there is another reading then the upper thermostat must be replaced. Turn on the faucet for the bathtub or allow the hot water to flow out and check the lower heating element. If it doesn’t come on the lower thermostat then you need to replace the same. When the temperature of the water dips or when the hot water flows out, the lower thermostat will shut off and you would observe the upper thermostat turning on the upper heater. Now check the upper heating element and observe the voltage. If you witness the upper heating element doesn’t come on then you ought to replace the upper thermostat.