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.
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 degrees 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.
To troubleshoot a thermostat:
- Shut off power to the heater at the electrical service panel and post a sign warning others NOT to turn it on.
- Unscrew and remove the electric water heater access panel.
- Using a small screwdriver, turn the thermostat dial counterclockwise to lower the temperature, or clockwise to raise it. If the water heater doesn't maintain the proper temperature, test the thermostat.
- Disconnect one wire to the upper thermostat to test it. Set a multimeter to RX1 (resistance times 1) and touch a probe to the thermostat terminals as indicated in the owner's manual. Depending on the model and the terminals tested, the tester should show 1 (infinity, open) or about 0 (closed).
- Test the lower thermostat in the same manner.
- If necessary, replace the thermostat. Unscrew it from its mounting and install one of the same model, size, and rating. Once you install it, adjust the thermostat following instructions in your owner's manual.
To test and replace a heating element:
- Turn off power at the Electrical Service Panel and post a sign warning others not to turn it on.
- Remove the access panel on the electric water heater.
- Disconnect one of the element wires and set a multimeter to RX1000 (resistance times 1,000). Touch one probe to an element mounting bolt and the other to each element terminal screw, in turn. If the tester displays anything but infinity (open circuit), replace the element.
- If necessary, set the multimeter to RX1 and touch the probes to the terminal screws. If there is any resistance reading at all (closed circuit), then the element is good. If not, replace it. Both upper and lower elements are tested in the same manner.
- To remove the element, first drain the heater.
- Disconnect the remaining element wire. Remove the mounting bolts holding the element in place. Remove the element.
- Replace the heating element with one of the same model, shape, and rating. Make sure you also replace any installation gaskets.
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