Why does the temperature of my hot water fluctuate?

In an electric water heater, the upper and lower thermostats must fit snug against the side of the tank to sense and regulate the temperature correctly. Turn off the power to the water heater and remove the access covers to check the thermostats' positions. Adjust the thermostat brackets if necessary to keep the thermostats snug against the tank.

A failed thermostat or heating element in an electric water heater can also cause hot water temperature fluctuations. If water temperature fluctuates below the set temperature, check for failed heating elements and thermostats. If the water heater tends to overheat the water, find the cause of overheating. Replace any failed thermostats and broken heating elements.

Sediment build-up at the bottom of the tank can cause hot water temperature fluctuations. If it's been more than a year since you drained sediment from your water heater tank, now's the time to clear sediment from the tank. A broken dip tube that carries cold supply water to the bottom of the tank will cause temperature fluctuations. Replace the dip tube if broken. Some water heaters don't have a replaceable dip tube. If you can't replace the dip tube, replace the entire water heater.