AO Smith Water Heater Error Code E02 [Why + How To Fix]

The main reason why the AO Smith water heater error code E02 pops up is a tripped ECO. It happens when the water temperature exceeds a certain limit. You can fix it by pressing the reset button.

However, that’s not always the case and the error code can come up even after resetting the heater. The other common reasons behind getting this error code are:

  • Defective Thermostat
  • Shorted Heating Element
  • Burned Out Connector
  • Faulty Control Board
AO smith water heater error code E02

You’ll learn how to reset the ECO to get rid of the error code and also solve the other issues in this guide. So, let’s dive in!

Table of Contents

AO Smith Water Heater Error Code E02 [5 Easy Fixes]

We’ll discuss why the error code E02 comes up on your AO Smith water heaters along with their fixes in this section.

Note: You can also read our guide on why AO smith water heater won’t light Or stay lit & how to fix it.

1. Tripped ECO

The ECO or the Electric Cut Off is a safety device that automatically shuts off power to the heater when the water temperature is too high. Did you turn up the temperature settings before your heater started displaying this error code?

If you did, then, this must be the issue. According to the default factory setting, the heater runs well at a temperature of 120°F or 49°C.

If you set the heater to a temperature higher than 160°F, the water becomes too hot and it can scald you. So, the ECO gets tripped and shuts off the operation of the heater.


The first thing you have to do if you see the error code E02 come up is reset the ECO. Nine times out of ten, a tripped ECO will be the issue. Resetting it will solve the issue.

It’s incredibly easy to reset the ECO and you can do it on your own. Follow these steps to do it:

  • Turn off your water heater by flipping the circuit breakers of the heater. Let the heater cool down completely.
  • Remove the upper access panel of your water heater using a screwdriver and fold the insulation.
  • You’ll see a red reset button. Press it gently and you’ll hear a clicking sound that indicates the switch was tripped and the reset is complete.
  • Unfold the insulation and put the upper access panel cover back on. Turn on the heater by flipping the circuit breakers back on.

The water heater should operate fine now. Make sure that you don’t set the temperature too high from here on. Otherwise, it can trip the ECO and you’d be facing the same issue again.

Here are some tips to help you use your AO Smith heater at the right temperature without tripping the ECO:

  • Adjust the temp setting in Fahrenheit and Celsius which should normally be 120°F (49°C).
  • Don’t let it be too high. Decrease the temp if it is 140°F or 150°F (60°C or 65°C). The standard mode permits you to reduce and increase the water temp
  • But it is best to keep your temp below 150°F (65°C) so that the limit switch doesn’t trip.

If you didn’t hear the clicking sound when you pressed the reset button, it means the ECO wasn’t tripped. In that case, it’s obvious that something else caused the issue. If the error code comes back on again, that also indicates other issues. Keep reading to continue the diagnosis.

2. Defective Thermostat

The next most common reason why the error code E02 comes up in your AO Smith water heater is a defective thermostat.

Normally, the thermostats allow to heat up accurately all the heating elements at once. An electronic AO Smith water heater has two thermostats that control the two heating elements.

defective ao smith thermostat

Such as; one is an electronic thermostat for the upper elements. Another is the thermistor, which is located back of the lower access panel. The thermistor acts as a resistor to detect temperature. Both heating elements are controlled by their individual thermostat.

Unfortunately, if either of the thermostats is faulty, the heater won’t work properly. Because a couple of wires may be shorted and keeps heating the water when it’s not supposed to. 

The thermostat signals the heating element to stop heating the water when it reaches the set temperature. But when you have a faulty thermostat, it keeps on heating the water even after the desired temperature has been reached.

That’s why, the top limit safety switch trips, and your heater will show an error code E02. Let’s know how to fix the defective thermostats.


If the thermostats turn out to be bad, you have to replace them. Here’s how you can go about diagnosing and replacing the thermostats:

  • Use a multimeter to test electric continuity. In this case, you’ll find the upper and lower terminals at the left and right on the electronic thermostat, which are connected to the heating elements.
  • Now, remove all the wire connections from the terminals. Place the probes on the terminals accordingly. Verify if the thermostat is continuing. If you have the continuity, it is performing well. Repeat the process to check the other one.
  • But, if either thermostat or both are not performing well. Replace it/ them with a new one immediately.

Remember: Match the number of the parts before purchasing any intake of one thermostat or thermistor. Because the high-limit switch is integrated with the thermostats. In this case, the heating elements may be short-circuited because of mismatching the parts’ numbers.

3. Shorted Heating Elements

When any of the two heating elements gets shorted, it can heat the water too much and cause the ECO to trip. The E02 error comes up on your AO Smith water heater when that happens.

Most AO electric water heaters have two heating elements. One is at the top and another is down towards the bottom of the water heater. The system runs power through each element.

 shorted Ao smith water heater heating elements

The heating elements mainly fail to operate when the high resistivity is unable to resist much heat. The above condition works as a safety measure to prevent hot wiring from grounded through the panel. 

But when a loose wire connection has slipped off a terminal can cause a heating element to stop operating. Therefore, the high-limit switch or thermostat may maltreat if the heating element is grounded or shorted and cause the error code.

You have to test the heating elements to know whether they’re working properly. Follow these steps to do the test:

  • Flip the circuit breakers leading to the water heater to turn off the power supply.
  • Remove the upper access panel with a screwdriver, fold the insulation, and remove the plastic cover.
  • Make sure the power is off by checking the screws of the thermostat with a noncontact circuit tester.
  • Take out the power wires of the heating element and measure the resistance at the two screws with a multimeter.

If the reading is not in the range of 5 to 25 Ohms, it means the heating element is faulty. You have to check both the heating elements following this process.

It’s possible that only one of them has gone bad and caused the error code. If they are within this range, that means nothing is wrong with them and something else is causing the error code.


If the diagnosis revealed that you have a bad heating element, you need to replace it. Follow these steps to do it:

Step 01 – Remove The Old Heating Element

  • Turn off the power supply to the heater and wait for it to cool down.
  • Open a hot water faucet and let it run until you get cold water from it so that you don’t hurt yourself later on.
  • Drain the water heater to remove the water in the tank.
  • Remove the access panel in front of the heating element you want to remove.
  • Unfold the insulation and take off the thermostat cover.
  • Remove the power wires from the heating element you want to replace.
  • Unscrew the bad heating element with an element wrench.

Step 02 – Install The New Heating Element

  • Clean the threads of the tank before putting in the new heating element so that it can fit well.
  • Insert the new heating element and lubricate the gasket of the new heating element so that it doesn’t get damaged when you tighten it.
  • Use the element wrench to tighten the heating element.

Step 03 – Test For Leaks

  • Put everything back together and make sure the tank is completely filled with water before you turn the heater back on. Turning on the heater before filling the tank with water can also make the heating element short out. So, steer clear of doing that.
  • Check for leaks. If there are no leaks, you can turn on the power to the heater. If there are leaks, you have to do the installation again correctly so that no water comes out of the heater.

That’s how you can replace the heating element by yourself. If you can’t install the heating element such that there are no leaks, you have to consult a qualified technician for it.

Make sure you get the right heating element for your heater by looking at the wattage and voltage in the data plate. If you use the wrong heating element, it can get shorted again.

So, take your time doing the replacement. It’s an easy process and hopefully, the error code will disappear after you replace the heating element in your AO Smith water heater.

4. Faulty Control Board

You may also get an error code E02 on your AO water heater because of a malfunctioning main control board. When there’s anything wrong with the control board, the entire heater goes out of order.

The faulty control board can display any error code in this situation and stop the normal operation of the heater. The error code E02 is just an example of what could go wrong when the control board goes bad. It can also show other error codes.


If you have a bad control board, your only option is to replace it. You can’t repair a control board. As it is a highly sensitive component that controls the heater and there are so many wiring connections attached to the control board, we don’t recommend you mess around with it.

Consult a qualified technician to diagnose the control board and replace it if needed. If a visual inspection shows burned-out parts in the control board, then you can conclude that you have a bad control board.

In that case, you can just hire a technician for the replacement. But if you’re not sure what’s wrong, it’s better to let a professional handle the complete job.

The good news is that AO Smith will cover the costs if your unit is under warranty. Otherwise, be prepared for a hefty bill.

5. Burned Out Connectors

Of all the issues we’ve discussed in this guide, burned-out connectors are the least likely to occur. But they lead to the error code E02 from time to time and that’s why you need to know about this issue.

Check the connectors on the control board and look at their condition. It’s possible that they were damaged if there were temperature spikes in the thermostat


You should be able to tell if the connectors are burned out by doing a visual inspection. If any of them are loose or burned, you have to replace them to clear the error code.


What are the common problems of the AO Smith water heater?

There are the most common problems with the AO Smith water heater. For example, no hot water, too hot water, no pilot light or power, taking too long to get hot water and high temperature, etc.

Why has my AO Smith water heater stopped working?

Your water heater may not work if the gas valve isn’t open. If the gas valve doesn’t work, the burner won’t light, and the heater fails to create heat. Ensure the valves are open and the ignition system is performing properly.

What is a thermistor?

A thermistor is a thermally sensitive resistor that is used for measuring temperature. Its resistor can fluctuate fast and reliably with temperature.

What is the ideal temperature of an AO Smith water heater?

The ideal temperature of the AO water heater is 120° Fahrenheit. You can change the temp up to 150-160° F. but there is a risk of overheating. So, set the temperature to less than 140°F to be on the safe side.

How can I adjust my AO Smith water heater?

Turn the temp dial clockwise to increase the temperature and turn the dial counterclockwise to decrease the temperature. But keep in mind that the temperature on both thermostats should be the same.


Now you know why the AO Smith water heater error code E02 comes up and how you can go about fixing it. Resetting the ECO will solve the issue in most cases and you’ll get hot water from your heater again.

But in the unfortunate occasions when resetting doesn’t work, you’re looking at a more serious issue. Luckily, you know how to fix them as well. Comment below if you have any more questions about clearing the E02 error code.

About William

William is the founder of He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

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