Cold water may be a common complaint with failing heaters, but some issues may also produce water that's too warm. Scalding hot water can present a burn hazard and can also potentially damage pipes and appliances. Recommendations for proper hot water temperatures range from around 120 degrees up to 140 degrees Fahrenheit.

If your water seems too hot, always start by checking your water heater's thermostat setpoint. It's usually a good idea to measure the water temperature at your taps, as well. Reducing the setpoint may temporarily help, but if your water temperature seems to be increasing on its own, it may be due to one of these three issues.

1. Failing Thermostat

Your water heater's thermostat effectively serves the same role as your home thermostats. Setting the temperature will determine how long the burner or heating element runs. Once the temperature reaches your setpoint, the water heater will stop running until the water in the tank begins to cool again.

The underlying mechanism used varies depending on whether your water heater uses gas or electricity, but a failure, in either case, can produce water that's too warm. Checking your thermostat's operation can be tricky, especially if you don't have experience diagnosing electrical devices. If adjusting the setpoint doesn't help, then it's probably time to call in a plumber.

Note that the temperature at your taps won't be the same as the temperature in the tank, so don't assume there's a problem if you measure something different from your setpoint.

2. Bad T&P Valve

Your temperature and pressure (T&P) relief valve should be located somewhere on the side of the tank, facing down. This valve opens when either the tank pressure or heat gets too high. You can test it by manually opening the valve, but stay clear of the tap since it will release hot water. A T&P valve that's stuck closed is a severe safety hazard, so contact a plumber immediately.

Note that there's likely another problem at play if a stuck valve is causing your water temperature to increase noticeably or if your valve must frequently open.

3. Electric Heating Element Issues

Electric heaters use heating elements at the bottom of the tank to keep your water warm. These are typically resistive-style heaters, and they require proper wiring to function correctly. Damaged wiring can prevent the heating element from shutting off, causing the water to get too warm. Over time, this will likely also cause the heating elements to burn out and fail.

Remember that extremely hot water poses a severe health hazard to anyone in your home and may also be an early warning sign of a dangerous water heater problem. If your heater seems to be ignoring your thermostat setting, then it's time to hire a water heater service professional to get to the root of the problem.

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