What causes an overheating electric water heater, and what can you do about it? Use this troubleshooting water heater article to repair overheating and avoid scalding burns.
Over time electric water heaters can develop various problems, including leaks, noise, bad smell, and most of these problems are explained in our troubleshooting guide. Some issues are easy to fix, some are not.
One of the situations, when you have to call in a professional is overheating.
While electric water heaters are equipped with energy cut-out devices to prevent overheating, the problem can still occur. Blistering hot water can happen anytime, and there are several reasons for it:
Note: Turn off the power (breaker or fuse), before you start working on a problem. Note that electric water heaters are hard wired directly from the circuit breaker, running on 115 or 220 volts. With the power off, check the wires for proper connectivity and damages.
When troubleshooting an overheating electric water heater, check the thermostat first as it might be accidentally tweaked up to the highest settings. Simply use the flat screwdriver and rotate the temperature dial counterclockwise to lower the temperature. Since water inside the tank is very hot, it might take some time (a few hours probably) before you can see the difference.
An optimal hot water temperature is around 120 degrees Fahrenheit.
One reason for overheating heating elements is when they are covered with limescale/sediments.
If you live in an area with a hard water problem, you might want to consider making it soft and spare your electric water heater from breaking and overheating.
Mineral deposits can affect your water heater's regular operation. Over time the bottom of the water tank, including heating elements, gets covered in sediments. A layer of sediments now acts as an insulator, making a water heater work harder to heat the water to the set temperature.
Because of all this thermal stress, the heating elements overheat, and water absorbs that extreme heat. Not long after overheating, one or both heating elements die.
The solution for this problem is to flush a water heater regularly to prevent sediment buildup. You can also install a water softener to prevent mineral deposits. Heating elements can be cleaned from sediments or replaced.
If you already have an issue with the sediments and a heating element is not operating correctly or at all, replace it. Once you replace a heating element, you will have normal water heating again, but your water heater won't last long due to the buildup – you might have to replace it. So, regular maintenance is very important.
You can also test the heating elements to see if they are good or not.
With the power off, wires removed from the heating element screws, and multimeter set to ohms, test only one element at a time. Touch with both probes the screws of the element. If the reading is close to zero, the heating element is ok. The procedure is the same for the other element.
Note that a shorted heating element can also cause overheating.
It is easy to test heating elements for a short circuit to ground. With the power off to the water heater, remove an access panel and insulation to access the heating element terminals.
Disconnect wires from heating elements. Set the multimeter to "ohms."
Touch the terminal (screw) of a heating element with one probe, and element flange with the other probe. There should be no reading. If you see any reading, the element is grounded and must be replaced.
If the thermostat is out of calibration or broken, this could lead to improper heating and high water temperatures.
A thermostat is designed to control the heating cycle of the heating elements. It turns the element ON or OFF, depending on the set temperature and actual water temperature. To read the temperature accurately, the thermostat must be sitting flush against the water heater tank. Make sure insulation is not interfering with a thermostat.
A thermostat comes with the red reset button (ECO), so it stops the power flow to the heating elements when activated.
If the thermostat or reset button fails to work as designed, heating elements could continue drawing power with no control, heating the water to extreme levels.
Visually check the wiring and thermostat for any visible signs of melting and burnt areas.
Thermostats are easy to replace and don't require tank draining, while heating elements do.
You can also test thermostats for proper work, but since they need to be performed with the power on, it is better to call in a professional to do it.
Sediment buildup is not good. It prevents proper heat transfer, creates an annoying rumbling sound, can clog the valves and cover components, reduce the life and performance of a water heater.
Temperature and pressure relief valves (T&P) are safety elements designed to release the buildup pressure from the water heater tank. When the temperature and pressure exceed the allowed levels, the valve opens automatically. The valve also includes a handle so you can manually release water. It comes in handy when draining/flushing a water heater.
It is recommended to check a T&P valve at least once a year to ensure that it has not become encrusted in limescale. You can test the valve by lifting the lever several times and release some water. Make sure the valve seats properly and there is no leak.
If a T&P valve is defective or stuck, the steam from a tank cannot escape resulting in overheating, element deformations, even injuries to the occupants if the steam or hot water is released. Buildup pressure inside the tank can also lead to deformations, even an explosion.
If you have any issues with a water heater not working or defective temperature and pressure relief valve, contact a qualified plumber to fix it.
Overheating is dangerous. High pressure and temperature could lead to scalding injuries, damage to your water heater, or even an explosion.
If extremely high hot water temperature or steam comes out of your faucets, or you hear the boiling sound inside the tank, don't hesitate, call a professional plumber.