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

Your AO Smith water heater error code E02 appears due to a high temperature, a clogged filter, a malfunctioning control board, a faulty thermostat, and so on.

Whatever the issues, you need a complete troubleshooting guide to fix them. So, we have figured out all the reasons behind your water heater error code E02.

AO smith water heater error code E02

In most cases, you can solve the problem by resetting the heater. Then, if the code reappears, go through the guide to detect each and solve your AO water heater problems instantly.

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

Here, we’ll focus on the AO Smith water heater error code E02 problems and easy tips you may face in using the water heater. Let’s go ahead to find out the troubles and get their simple solutions.

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

1. Too High Temperature

The highest temperature setting is one of the common reasons for Your AO Smith water heater displaying an error code E02.

According to the default factory setting, the heater suits to 120°F (49°C) to run well. Otherwise, it may maltreat if you set up the temp beyond it as recommended.

ao smith temp setting units

Functionally, there is a high limit switch safety mechanism that trips or shuts down when the temp is 150°F (65°C). So, the switch is also known as an Emergency Cut-Off Switch.

You can increase the temp if needed. But there is a risk of overheating and the limit switch getting tripped.

Then, you will get an alert message-E02 that indicates you need to repair the unit.


  • First, turn off your water heater and let it cool down completely.
  • Adjust the temp setting to 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.
  • Yet, if you are unable to fix the issue, there may have problems with thermostats or other parts.

Note: changing the temp setting is not a proper solution if the emergency cut-off switch trips. You must reset it before restating your water heater.

2. Defective Thermostat/Thermistor

A defective thermostat or thermistor is the next reason for appearing E02 error code on your AO Smith Water heater.

defective ao smith thermostat

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

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, it doesn’t work because a couple of wires may be too shorted which causes overheating.

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.


When your heater’s temp is alright but you are getting the error code E02 on your water heater, you should fix the troubles in the following ways:

First, get a screwdriver to remove the upper access panel of your water heater. Turn off the double circuit breaker of your electric AO heater. 

You can also remove the power of the wall socket. Use a multimeter to make sure there is no power on the top of the heater, as you are dealing with a 240-volt circuit.

Press gently on the high-limit switch reset button to reset it. Now, you will hear a ‘click’ if it’s tripped. At this point, you can restart your heater to ensure that the code E02 reappears. Hopefully, it won’t show the code if the temp and other related parts are fine.

Unfortunately, you may see the error code again if either the thermostat is defective. The high-limit switch’s tripping is a symptom of it.

To fix a defective thermostat, remove the cover to get access to the electronic thermostat.

Use a multimeter to test electric continuity. In this case, you’ll find the upper and lower terminals on the left and right of 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 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. Malfunctioning Control Board

You may get an error code E02 on your AO water heater because of a malfunctioning of the main control board or damaging computer module.

Mechanically, the main board controls the power supply to all areas of your heater. So, if it gets defective, it will shut down electricity to all the parts, including the breakers in your heater’s electric functions.

breakers in your heater’s electric functions

Unfortunately, the internal wiring components may have burned because of the spiking temperatures. However, this is a critical case of the heater that indicates your E02 code to repair the units.


Step 1: First, power off your water heater. Find out the control panel and have a sharp eye on it. If you find any minor issues with the control board, repair the burned, damaged, or failing components.

Step 2: You can simply try to reset the control panel. Here, you will find a red reset button near the thermostat or may be hidden behind the removal of the metal panel.

Step 3: After you find the red button, just press it and release it. Then, back to the electrical panel to turn over the breaker switch to the on position. Expectantly, you won’t see any E02 code on your water heater again.

Step 4: But if you detect any major problems there, replace a new control board or module. Because this part is not a serviceable part at all.

Step 5: For this purpose, you will be got a free service from your AO Smith service provider if you are under warranty still now. The team will inspect minutely what wrong is going with your water heater’s electric board. It will save you money and time.

4. Shorted Heating Elements

The shorted heating elements are also responsible for your AO water heater flashing an error code E02 on the screen. Most, AO water heater has two heating elements. One is at the top and another is down toward the bottom of the water heater.

The system runs power through each element. 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 from hot wiring 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, you will see the E02 code on the screen which means there is something wrong electrically.


  • First, test the heating elements. You’ll find the heating elements below the respective thermostats.
  • Secondly, turn off the circuit breaker dedicated to the water heater and remove the plug from the wall socket.
  • Then, remove the upper and lower access panel and all the wires from the terminal to test the heating element for continuity. As these elements typically have in the range of 10-15 Ohms, use a multi-meter Ohms test setting to detect their resistance.
  • If you find they have proper resistance, you must check an electrical short by following the steps.
  • Place a multi-meter probe on one terminal of the upper and lower heating element and the other probe on the metal body of your heater. If there is no continuity, the heating element has been shorted or grounded. Recheck both the elements in the same way if they could have been shortened.
  • Change or replace the shorted or defective heating element to fix the issues, as this is not a serviceable unit. 

5. Dirty/Blocked Filter

Your AO Smith water heater can display an error code- E02 due to the filters being dirty, old, or blocked. This hints that something is occurring electrically with the water heater.

replace the dirty water filter

In particular, pumping at low speeds, hard water, or dirty water can cause of other issues. When there is a problem between pumping and the filters, a low-pressure system can push air into tubes.

Plus, if you leave your filter for more than one or two weeks, it can significantly restrict water flow. Once air gets started in it, it may create bubbles that can intensely interfere with the water flow sensor. Finally, it results in tripping the code E02.


To make sure the filter is causing this problem, remove the filter. Then, if the water stops flowing, remove it and then wash or clear out the dirt and debris from the filters by using lukewarm water.

You can watch the below video on how to clear out dirty filters. Now, reconnect and tighten up the filters immediately. Yet, if you get the code E02 again, it indicates the filter is only responsible for obstructing water flow. Therefore, replace the filter to solve the problem.

How To Reset AO Smith Water Heater Easily

The E02 means that your AO Smith water heater is going through something wrong electrically. However, most of the heater’s error code-related problems may be solved only by resetting the appliance.

Before taking any steps, you can simply reset your AO Smith heater in the following ways to fix the above troubles.

  • Go to the electric panel on the exterior walls of the heater.
  • Find the breaker and turn it off.
  • Open the cover panel by removing screws and you’ll get a Red Reset Button near the thermostat.
  • Just press gently on it and release it. You will get a sound ‘click’ that indicates your water heater has been reset.
  • Finally, head to go to the electric panel to flip the circuit breakers to the on position.


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 is 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 the 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, a manual temp setting is best because of reducing the risk of scalding.

How can I adjust my AO Smith water heater?

To adjust the temperature, 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 set to 120°F. 


Now all the reasons are absolutely clear to you why the AO Smith water heater is displaying error code E02. So, whenever you are facing error code troubles, definitely, you can fix them by yourself if you follow the above troubleshooting guide.

Yet, if you face any other issues related to E02 codes, let us know, and feel free to drop us a comment in the box below. We’ll try to make out an instant solution ASAP.

About William

William is the founder of He has practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their units & saving their pockets. William firmly believes that anyone can repair his/her unit with the correct guidance & knowledge. More about us.

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