How to test electric water heater thermostat

An electric hot water heater has two thermostats controlling two separate heating elements — one in the upper half of the tank, one in the lower half. Usually, when the upper thermostat goes bad, you will have no hot water at all, while a bad lower thermostat makes itself known when there is only a small amount of hot water before the tap water goes cold. This is not a hard and fast rule, though, and it's best to test the thermostats to determine which one needs replacing.

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A common electrician's tool known as a multimeter is used to test the thermostats. Once you have determined the faulty thermostat, you can replace it and have your hot water heater working again.

Step 1

Turn the water heater circuit breaker off inside the main service panel.

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Step 2

Remove the upper and the lower access panels with a Phillips screwdriver. The access panels are on the side of the electric hot water heater and usually have an electrical warning label attached.

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Step 3

Pull away any insulation that is covering the thermostat and the heating element. Be careful not to pull any wires while moving the insulation.

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Step 4

Use a flat-head screwdriver to turn the temperature setting to the highest setting on the upper thermostat. Set the scale on a multimeter to the RX1 setting.

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Step 5

Place one probe on the left screw terminal with the white wire and one probe on the terminal directly above the white wire. The reading on the multimeter should show zero. Any other reading on the multimeter indicates a faulty thermostat.

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Step 6

Set the upper thermostat to the lowest setting using the flat-head screwdriver. You should hear a click from the thermostat during this process. Place one probe on the terminal above the white wire and the other probe on the terminal that the black wire connects to. Again, the reading on the multimeter should be zero.

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Step 7

Leave the upper thermostat in the lowest setting and test the lower thermostat. Use the screwdriver to set the lower thermostat to the highest setting. Touch one probe of the multimeter to each terminal on the lower thermostat. The lower thermostat has only two terminals. The reading on the multimeter should be zero.

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Step 8

Replace the faulty thermostat, and place the insulation back over the thermostats and the heating elements. Replace the access panel covers securing the covers with the retaining screws. Turn the circuit breaker back on to activate the electric water heater.

If you’re experiencing problems with the hot water in your home, one way you can troubleshoot your electric water heater is by checking its thermostats. Recalibrating or replacing a thermostat is a relatively simple repair, so it’s worth testing them before despairing that your water heater has heated its last shower. You can check your water heater’s thermostats using a multimeter, which is an electrical measuring tool easily purchased online or in any home improvement store.

Signs That Your Water Heater’s Thermostat Might Be Faulty

Most electric water heaters have two thermostats: an upper one and a lower one. The upper thermostat is the primary thermostat and is attached to the high limit switch, which keeps your water from getting dangerously hot. Depending on which thermostat is malfunctioning, you may see different symptoms:

• No hot water – This most likely indicates a problem with the upper thermostat.
• Not enough hot water – This most likely indicates a problem with the upper thermostat.
• Slow hot water recovery – This is another problem that can occur when the lower thermostat is malfunctioning.
• Water is too hot – Overly hot water can occur if either thermostat (or both) is set too high or isn’t calibrated correctly.
• High limit switch keeps tripping – If the red reset button on your water heater keeps popping out and needing to be reset, your upper thermostat could be malfunctioning. This would allow your water heater to keep heating the water to dangerous levels, which will trip your high limit switch.

If you notice any of these signs and you happen to have a multimeter, test your water heater’s thermostats to see if they’re the problem.

How To Test Your Water Heater’s Thermostat

To test your water heater’s thermostats, you will need a flathead screwdriver and a multimeter. With those tools at hand, follow the steps below:

1. Power off – Turn off your water heater’s breaker on your electrical panel.
2. Remove panels – Use a flathead screwdriver to remove the upper and lower thermostat access panels. The thermostats should be covered by a layer of insulation, so fold it out of the way and secure it temporarily with tape.
3. Upper thermostat test #1 – Using your screwdriver, turn the upper thermostat to its maximum temperature. Adjust the multimeter to RX1. Place one meter probe on the bottom left terminal. Place the other meter probe on the terminal screw #1 just above the #2 terminal. You should get a reading of 0. If you don’t get a reading at all, the thermostat is faulty.
4. Upper thermostat test #2 – Turn the upper thermostat temperature to the lowest setting. You should hear it click off. Place one probe on  terminal #1. Place the other probe on the bottom right terminal screw (#4). You should get a reading of 0. If you don’t get a reading at all, the thermostat is faulty.
5. Lower thermostat test – The lower thermostat is easier because it only has two terminals. First, use your screwdriver to turn the temperature all the way up. (The upper thermostat must be clicked off, which should have been achieved in step #4.) Place a meter probe on each of the terminal screws. You should get a reading of 0. If you don’t get a reading at all, the thermostat is faulty.

When you are finished, be sure to adjust the thermostat temperatures back to normal, replace the insulation, and screw the panels back on.

Expert Water Heater Repair in Dallas

If you find that your water heater’s thermostats are faulty, you’ll need a trusted plumbing company to repair or replace them. If you live in the Dallas area, your first call should be Frymire Home Services. Our expert plumbers will quickly get to the bottom of your water heater problem. We can replace your water heater’s thermostat or diagnose any other water heater issue. With more than 65 years of plumbing service, we have the skill and experience to restore proper function to your water heater.

For water heater repair or a new water heater thermostat in Dallas, count on the skilled plumbers at Frymire Home Services. Call us today at 469-346-4999 or contact us online!

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