How to Use a Multimeter to Check the Voltage on a Water Heater

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Checking the voltage on a hot water heater is going to require the careful use of a device called a multimeter. Use a multimeter to check the voltage on a hot water heater with help from an area manager for Roto-Rooter Plumbing & Drain Service's Independent Contractors Division in this free video clip.

Part of the Video Series: Hot Water Heaters
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Video Transcript

A multimeter is a useful tool for both electricians and plumbers. I'm Dave Jones, master plumber for Roto-Rooter Plumbing and Drain Service. A multimeter device can do a lot of things that most people don't know how to use many of its functions. A multimeter is used to detect voltage, amperage and continuity in electricity. You can also determine resistance, how many amps an appliance is drawing and much more. I'm going to show you how to use a multimeter to check the voltage on your water heater. The first step is to turn off the power at the breaker box or the disconnect box. Be sure to post a notice that you are working on the water heater and the breaker switches should not be messed with. You wouldn't want someone to flip on one of the switches while you are working on the appliance or you could get a terrible shock or killed. Next, take off the two cover plates on the side of the water heater tank. Remove the insulation and the plastic protective covering that is surrounding the thermostat. Next, you'll need to turn on the electricity to the water heating. On the multimeter, make sure it is rated for more than 240 volts of electricity. On the bottom there should be a tag listing the multimeter's range. A standard multimeter usually will handle 0 to about 600 volts. Your next step is to check to see if the water heater is getting any kind of voltage by turning the multimeter dial to where you have a V with a sideways S symbol next to it. This means voltage alternating current. Under the voltage settings, adjust the dial to the higher than 240 volt setting. Next, you want to plug the red probe into the corresponding port that is for the voltage and plug the black wire into the port that is labeled common or it might be abbreviated to read COM. At this time we'll be checking to see that our upper thermostat is getting power by touching the probes to the most upper terminal screws on the thermostat. It doesn't matter which probe touches which screw because this is alternating current. If the water heater is getting power, your meter's digital display should show it getting 240 volts. An analog display will also show the 240 volts. So if your water heater is not getting the full 240 volts, there could be several reasons for this and you'll have to work your way back from the thermostat to the circuit breaker box or the point of power. You might have a bad wire or a breaker somewhere that is preventing the appliance from getting all the power that it requires to operate reliably. That's how you use a multimeter device to test the voltage on your electric water heater. I'm master plumber Dave Jones with Roto-Rooter Plumbing and Drain Service. Thanks for watching.


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