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Most electric water heaters have two elements and two thermostats. The thermostats control the elements to heat the water efficiently. As hot water is drawn from the tank at the top, cold water is added to the heater from the bottom through a fill tube and is heated by the bottom element. When the water at the top of the tank begins to cool, the top element turns on.
If water is drawn from the tank continuously, the lower element will not have time to heat the water sufficiently, and you will gradually notice the water getting cooler. The top element will turn on again until the water at the top of the tank is hot. Once the water in the tank is heated, the elements only turn on to keep the water hot. -
The thermostats are located just above the heating elements. As the water temperature fluctuates due to convection, cooling or use, the thermostats turn the elements on and off to keep the water in the tank at a steady temperature.
Each thermostat has its own control dial. Both thermostats should be set to the same temperature. The usual setting is 120 degrees, but homes that have a dishwasher may need to set the thermostats to 130 degrees if the dishwasher lacks a heating element.
The upper thermostat controls the lower thermostat. As the water at the top of the tank reaches the thermostat setting, the upper thermostat sends power to the lower thermostat and turns off the upper element. The lower thermostat turns on the lower element, which heats the water at the bottom of the tank until the bottom thermostat shuts it off.
If some water is used from the top of the tank, cold water enters the bottom of the tank. Since the upper thermostat left the lower thermostat activated, the lower thermostat turns on the element again and heats the cold water that entered the tank. However, if the hot water from the top of the tank is used up, the upper thermostat will turn off the lower thermostat and turn on the upper element.
Thermostats have a safety switch, usually a red button. If the water temperature goes too high, the safety switch turns off the electricity, and the button must be reset before the water heater elements will work. - Some water heaters have only one element and one thermostat. They are small and may operate at a 120 volts, as opposed to 240 volts. Single-element heaters take longer to bring the water to temperature and don't supply as much hot water. They are typically used in small residences where only one or two people live.
- The anode is a device that prevents the electric water heater from being destroyed by corrosion. It is inserted from the top of the heater and corrodes instead of the water heater.
