My Water Heater is Getting too Hot

There is such a thing as too hot water. If your water heater has suddenly begun to send out a screaming hot flow, it’s likely due to one of the reasons we discuss here. We’ll also share how to change the thermostat temperature on tank style and tankless water heaters.

Reasons your water heater is getting too hot

Water heaters, whether they’re a traditional tank or newer tankless, on-demand style, are meant to last with regular water heater maintenance and timely repairs. Tank units can last up to a decade while tankless units may last up to two decades. But, if you experience any of these reasons for excessively hot water, contact a trained plumber for repairs.

Broken Thermostat

Starting with the thermostat is always a good idea. It operates similarly to the HVAC thermostat by telling the water heater how long and to what temperature the heater should warm the water inside the tank. Therefore, if the thermostat malfunctions, by extension, so does the water heater. Test the thermostat’s function by lowering the set temperature 15 to 20 degrees. Wait two to three hours to check the hot water temperature at a faucet or tap with a thermometer. Keep in mind that the further away a tap is from the water heater, the cooler the tap water will be due to heat transfer loss. But, if the water temperature doesn’t match or isn’t close to the newly set temperature, the issue is likely in the thermostat.

Misaligned Thermostat

If the thermostat isn’t correctly aligned and mounted flush to the tank, it can’t properly read the water temperature. Depending on the water heater’s age, it’s possible for the thermostat to work itself loose through vibrations and occasional bumps into it. Use a standard screwdriver to loosen the mounting screws, realign, then secure the thermostat in place against the tank.

Mineral Buildup

Nearly 85% of the United States has hard water. This naturally occurring water leaves behind mineral deposits, such as calcium, magnesium, and limescale on surfaces. As the deposits build inside the water heater tank, they interfere with the unit’s ability to regulate the water temperature. An annual water tank flush as part of water heater maintenance is the best way to avoid excessive mineral buildup. By removing the deposits, you’ll reduce the chance of overheating the water while helping the entire unit work more efficiently and effectively.

Faulty Heater Element

All water heaters use a heating element to warm the water, but electric-fueled units rely on one or two electric heating elements. These components will eventually begin to ground or fail with age and wear; when this happens, the element doesn’t turn off and excessively warms the water. It’ll eventually fail and leave you without hot water until it’s repaired and replaced by a trained plumber.

Issues with the Pressure Relief Valve

The temperature and pressure relief (TPR) valve is found on the side of most water heaters. It usually sits idle unless the water temperature and/or steam pressure inside the tank begins to reach unsafe levels. Then, the valve opens and allows a small amount of pressure and water to leave the tank until the levels recede and the valve closes. But, if the valve becomes blocked or otherwise malfunctions, it won’t open as needed and the tank could potentially burst. Check the TPR valve by lifting it up and down several times. If you hear a gurgling noise, or see a tiny stream of water or steam exit, it’s working. If not, or you hear a different noise, contact a plumber immediately.

How to Change the Water Heater Thermostat

Ripping hot water may feel good for a few seconds, but that’s all the time needed to suffer burns or scalds, especially for young children or elderly adults. Most water heaters are set to 140 degrees Fahrenheit upon installation. The temperature can be lowered but shouldn’t go below 120 degrees Fahrenheit — any lower and illness-causing bacteria have an environment to grow. But, changing the temperature on a water heater is relatively easy.

Gas Water Heater

  1. For older units, look for a dial near the bottom of the tank — it’ll most likely be used to adjust the temperature. Newer gas water heaters have the thermostat installed behind an access panel and layer of insulation on the tank.
        1. Turn off the water heater’s power source at the circuit breaker.
        2. Look for the access panel and use the screwdriver to unscrew it from the tank.
        3. Remove any insulation inside the panel (there should be some.)
        4. Adjust the thermostat temperature with the screwdriver.
        5. Replace the insulation inside the panel and reattach the panel.
        6. Turn the power back on at the circuit breaker.
        7. Relight the pilot light if necessary.
        8. Wait two to three hours to test the water temperature and further adjust the thermostat, if necessary.

Tankless Water Heater

Look for a digital control panel on your tankless water heater — it may look similar to your HVAC thermostat. This panel will have the water heater’s thermostat and the temperature can be adjusted up or down with push buttons. Contact Moore Home Services for timely plumbing repairs and to avoid burns and scalds.