Who used up all the hot water?! Maybe nobody. Maybe your electric water heater needs fixing. Once you know how it works and how to diagnose it, you can fix it and save some money. (If your home is not equipped with an electric water heater, see Gas Water Heater Fix-It Guide .)

How Does It Work?

Components of a typical electric water heater.

A water heater is an apparatus for heating water and then storing it for later use. A residential water heater typically warms water to a temperature between 120° and 140°F. When a hot-water faucet is opened, hot water flows from the top of the tank toward the faucet, and cold water enters the tank to replace it. In an electric water heater, the thermostat senses a drop in the water's temperature and completes an electrical circuit to the heating elements. Electric water heaters usually have both an upper and a lower heating element; each is controlled by a separate thermostat. Once water in the tank reaches the set temperature, the thermostats stop the flow of electricity to the heating elements. In addition, an anode (magnesium) rod attracts impurities in the water that would otherwise attack the metal tank.

Fix-It Tip

Many homes are located in areas with hard water. The contaminants in the water supply build up over time, creating a layer of sediment on the bottom of the water tank, hindering the heater's performance and shortening its life. You can slow this process by softening the hard water and by lowering the temperature to 130°F or less. Also, to minimize sediment, purge your tank every few months. Simply drain off 2 or 3 gallons of water from the tank, then let it refill.

What Can Go Wrong?

Because electric water heaters are simple in operation, few things can go wrong with them, and solutions are relatively easy to figure out. Heating elements and thermostats fail. The high-temperature cutoff may trip. The pressure relief valve may malfunction. Sediment can settle in the tank.