Electric water heaters commonly have two thermostats: an upper water heater thermostat and a lower thermostat. The bottom thermostat heats the water as it comes into the tank, while the upper thermostat helps to maintain the water temperature.
If you find your hot water runs out quickly, it may be due to a faulty lower thermostat. The best way for a homeowner to test a bottom water heater thermostat is to check the thermostat’s resistance and ensure the thermostat is opening and closing properly.
Do this by powering the water heater off.
Step #1
Shut off the electricity to the water heater at the circuit breaker. Go to the water heater and remove the screws securing the lower access panel to the water heater using a Phillips-head screwdriver. Pull the access panel off and move the insulation away from the thermostat.
Step #2
Find the red reset button on the lower thermostat. If the button is out, simply press the button in, and the thermostat should work. Power surges sometimes cause the reset button to trip and cut off power to the thermostat.
Step #3
Turn the dial on your multimeter to measure ohms and zero out your meter. Hold the metal leads together and turn the adjustment dial until the scale reads zero on most multimeters.
Step #4
Place a multimeter probe on each of the thermostat terminal screws. The lower thermostat has only two screws. Rotate the temperature adjustment screw clockwise to raise the set point. The multimeter scale should go to zero. Turn the screw counterclockwise, and the scale should begin to get a reading of infinity.
Step #5
Replace the thermostat if it fails this test. The thermostat is stuck in the closed position. If the thermostat passes the test, the problem is elsewhere in the system.
Indications of Faulty Water Heater Thermostat
A faulty thermostat in your water heater can lead to various problems, impacting the availability and temperature of hot water in your home. Identifying these issues early is crucial, as replacing a defective thermostat is significantly more cost-effective than a full water heater replacement.
Here are the key indicators that your water heater’s thermostat may require replacement:
- Absence of Hot Water: A complete lack of hot water is often the most apparent sign of a thermostat failure, preventing the heating element from engaging.
- Rapid Depletion of Hot Water: If you notice that hot water runs out quickly, the thermostat may be failing to maintain the set temperature, causing the heater to underperform.
- Overheating: Water that is consistently too hot could indicate that the thermostat is stuck in the “on” position, leading to unsafe water temperatures.
- Extended Heating Times: When the water heater takes longer than usual to heat the water, this could be a sign of a thermostat that is not correctly regulating the heating cycles.
- Frequent Tripping of the High-Temperature Limit Switch: Constantly needing to reset the high-temperature limit switch suggests the thermostat is causing the water heater to overheat, triggering the safety mechanism.
Other symptoms, such as leaks from the top of the unit, typically point to aging components rather than thermostat issues and could signal the need for a full system upgrade.
