Some water heaters may also by 208 Volts, but 240 is the most common voltage for a home water heater.

Heaters are powered with either a 1-pole or 2-pole circuit breaker. A 120-volt heater always uses a 1-pole circuit breaker, while a 240-volt heater always uses a 2-pole circuit breaker. Note that hits only apply to residential settings. In a commercial setting, you can actually have a 208-volt or 277-volt circuit, for instance. Larger water heaters tend to be 240-volt. In fact, most homes nowadays are built with 240-volt heaters. [4] X Research source Don’t assume that this is the case for your home, though—it’s always better to check and be safe.

On the flip side, it’s never a good idea to install a 120-volt water heater to a 240-volt circuit. The circuit will be too powerful for the heater and completely break it. Operating a 120-volt water heater on a 240-volt circuit may also start a fire in your home.

Tap your voltage tester against a plugged-in cord first to make sure that it’s working correctly. If the device beeps, go back to your circuit breaker and make sure that the right switch is turned off.

Some water heaters may not let you pull out the insulation completely. In this case, tape it to the side of the heater tank so you can clearly see all the wires and terminals. [9] X Research source Certain water heaters may also have plastic casing on top of the wires and terminals. Be sure to pull this cover off before you start testing. [10] X Research source

Double-check the bottom of your multimeter to see how many volts it can handle. You don’t want to accidentally damage your multimeter by overloading it! If your multimeter is set to less than 240 volts, it won’t be able to properly register the voltage of your water heater.

Make sure that you aren’t touching or handling the metal ends of the probes, or else you might get shocked. For extra protection, slide on a pair of rubber insulating gloves that are cleared for at least 240 volts of shock. This way, you’ll be protected even if you touch a live terminal or wire. [15] X Research source

If no voltage number shows up on your device, you may need to get it repaired.