How to Test an Electric Water Heater Thermostat with a Digital Multimeter

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How to Test an Electric Water Heater Thermostat with a Digital Multimeter

How can you tell that the thermostat of your electric water heater is faulty? Most importantly, how can you test the thermostat using a digital multimeter. A thermostat is a device that regulates temperature automatically. It performs actions such that the temperature of a given system maintains near an appropriate setpoint.

Usually, an electric water heater has one or more thermostats controlling two heating elements. They are typically positioned one on the lower half of the tank and the other on the upper part of the container. Some signs can tell you that your thermostat is faulty.

When the water heater does not produce hot water, the upper thermostat could be damaged. When the water tank does provide hot water or not near the expected temperatures, the lower thermostat could be faulty. Again if the circuit breaker trips continually, chances are that the thermostats have a short circuit.

Once you note the thermostat is faulty, you can use a digital multimeter to check the problem.

A digital multimeter can be used to check on the current, voltage, and resistance. Below are steps to follow when measuring resistance, voltage and current using a digital multimeter.

Measuring resistance using a digital multimeter

​Here are steps to follow:

  1. Switch off the power breaker that powers the hot water
  2. At the bottom of the water tank, remove the water metal to reveal the thermostat of the water heater.
  3. If your water heater has plastic and insulation cover pull them out
  4. Ensure the power is off with a non-contact voltage detector
  5. Identify the ends of the two elements inside the open panel
  6. Position the multimeter to the minimum setting for ohms resistance
  7. Unplug one wire of the thermostat
  8. Plugin the probes into the required ports. Usually, there are several ports in a multimeter. They might be labeled as COM, and in others, the ohms sign is visible.
  9. Switch on the multimeter
  10. Choose an expected range such that the best readings can are observed.
  11. Measure by applying the probes to the thermostat under the test.
  12. Test the second thermostat if you find out the first one is working
  13. Fix back the wire and cover the water heater’s exposed panel
  14. Switch off the multimeter to save on energy

Measuring the voltage of a water heater thermostat using a digital multimeter

At times the water from your electric heater could be cold and the heater not functional despite the power being on. In such a case, there is a need to carry out a voltage test. Here are the steps to follow while measuring the voltage of your heaters’ thermostat.

  1. Switch off the power breaker that power the water heater.
  2. At the bottom of the water tank, remove a metal plate to reveal the thermostat you suspect is faulty.
  3. Pull out the insulation and plastic of your water heater if it has one.
  4. Check if the power is off by using a non-contact voltage detector, thus reducing the risk of electrocuting.
  5. On the multimeter plugin, the probes into the resistance ports.
  6. Switch on the multimeter.
  7. Set the multimeter range to read the most substantial expected value. The digital millimeters can function with both ground and live values on the probing.
  8. Begin by probing the minimum voltage points.
  9. Secondly, probe the maximum voltage point.
  10. If a must, adjust the range switch to get the accurate reading.
  11. Note down the readings.
  12. Make the next observation or switch off the multimeter if testing is complete.

Measuring current of an electric water heater thermostat using a digital multimeter

Current is the rate at which charge passes through a certain point in a circuit. When your thermostat is faulty, you can use a digital multimeter to test the current flow. Below are the steps to follow when measuring the current of an electric water heater thermostat using a digital multimeter.

  1. Turn off the power breaker that powers your water heater.
  2. At the bottom of the electric water heater, remove the metal plate to show the thermostat you suspect is faulty.
  3. If your water has a plastic and insulation covering, pull them off.
  4. To avoid the risk of electrocution, check if the power is off by using a non-contact voltage detector
  5. Turn on the multimeter.
  6. Insert the probes into the correct connection. In this case, use the resistance sockets.
  7. Set the multimeter switch to measure current. Make sure the highest range goes above the anticipated reading. Avoid overloading your multimeter. It is advisable to select a range that is too high.
  8. Note the readings on the screen of the multimeter.
  9. Switch off the multimeter to save on power.

Measuring continuity of an electric water heater using a digital multimeter

Below are the steps to follow:

  1. Switch off the power breaker that supplies power to the water tank.
  2. Open the water tap, and let the water flow till it’s cold. During testing, make sure that the water in the tank is not above the lukewarm level.
  3. Detach the wiring access with a screwdriver at the top of the heater.
  4. Position the multimeter to the right range.
  5. Remove the access panel for the thermostat.
  6. Remove the electrical wires of the thermostat by loosening the terminal screws.
  7. Connect the leads into the thermostat under test, making sure the circuit is off.
  8. Once a complete continuity is detected, the multimeter will beep, but if there an open circuit, there will be no beeping.
  9. Once the readings have been recorded, switch off the multimeter to save on battery.

Final Thoughts

A digital multimeter is easy to use and gives accurate readings. After noting down the readings with your digital multimeter, it is crucial to switch off the meter to save battery. It is also essential to put on shoes that have rubber soles and rubber gloves to reduce the possibility of electrocution. Also, for safety, use insulated tools. Hopefully, this article will help in using a multimeter to check on voltage, continuity, resistance, and current of the thermostat of your water heater.

About the Author Dan

Just a random guy who likes to build things. Providing tool knowledge, appliance/device testing tips, and DIY project info in an easy-to read & non-intimidating style.