AO Smith Water Heater Code E02

AO Smith Water Heater Code E02 [How To Fix]

This is a troubleshooting guide on AO Smith Water Heater Code E02. What I am going to discuss in this article: 

  • 5 common reasons that cause the heater to flash the error code e02
  • The troubleshooting steps you need to follow to solve the water heater issue
  • And a lot

Without further ado, let’s dive in to explore the way of clearing the diagnostic code ‘e02’. 

Table of Contents

AO Smith Water Heater Code E02: Why Does This Error Code Pop Up?

Error code ‘e02’  on AO Smith Water Heater means the water temperature exceeds the high limit. Your AO Smith Electric Water Heater will throw this diagnostic code due to a tripped ECO button, bad heating elements, and faulty electronic thermostat. 

Trying to reset the ECO button before doing anything can clear the error message ‘e02’ from the display. If the error code returns after resetting the reset button, you should look for other issues like bad heating elements and faulty thermostats. 

Nonetheless, a bad computer board or damaged connectors leading to the computer module can also cause the unit to flash error code ‘e02’. 

Below, I will break down everything you need to know to clear the error message ‘e02’. So, keep scrolling. 

01. ECO Button Gets Tripped

Like other electric water heaters, AO Smith Electric Water Heater also has a ECO (energy cut-off) switch. When the water temperature of the unit exceeds the safety level, this button cuts off electric supply to the unit to avoid potential hazards. 

In short, a tripped ECO represents an overheated tank. And the unit will beep the fault code ‘e02’ to let you know the water temperature crosses the high limit. 

How To Fix: 

Reset the ECO first to fix this issue before making any replacements. Going along with the following steps will help you reset your AO Smith Electric Water Heater: 

1. Turn off electric power to the unit by flipping the water heater circuit breaker. 

2. Remove the upper access panel using a flat head screwdriver and gently fold away the insulation, which will expose the red reset or ECO button. This is how the reset button looks like: 

This is the reset button

3. Press the reset button and you will hear a click. If the reset button clicks, understand you reset the water heater successfully. 

4. Put both the insulation and the upper access panel back into their places. 

5. Turn on the electric power at the circuit breaker.

02. Bad Heating Elements

Grounded heating element

If resetting the ECO doesn’t bring any luck to you and the error code E02 returns, my next suspicion goes to the heating elements. 

A shorted or grounded heating element can cause extremely hot water. You can easily determine if the heating elements get grounded. If the T&P Valve (temperature and pressure relief valve) drips a large amount of hot water, understand the heating element gets electrically shorted. 

In this case, you must replace the bad elements to avoid the too hot water issue. 

How To Fix: 

Observing the sign of a grounded or electrically shorted heating element doesn’t mean you need to replace it without inspecting it. First, test the elements electrically to ensure it’s at fault.  

To test the heating element, turn the electric power off to your water heater at the circuit breaker. Then, remove the upper access panel and gently pull away the insulation. 

Now, get a multimeter and place its lead between the two terminals on the heating element. A healthy heating element will give a reading between 5 to 25 Ohms. Otherwise, you must replace the heating element. 

Follow the same procedure to test the lower heating element as well. You must drain the water heater to change the element. So, attach a garden hose to the drain valve at the bottom of the unit and drain the water. 

Once you drain the tank, use an element wrench to remove the heating element. Then, install a new one, fill the tank, and check for leaks. Finally, put everything back into its place and turn the electric power on to your water heater. 

03. Faulty Electronic Thermostat

A malfunctioning thermostat

A defective thermostat can also be the culprit behind this issue. If the thermostat is malfunctioning, it can cause the water to get extremely hot. And you already know the AO smith water heater will flash the fault code e02 if the water temperature surpasses the high limit.  

How To Fix: 

Before heading over to replace the thermostat, test the electronic thermostat electrically. The below video will help in inspecting the thermostat correctly: 

Don’t hesitate to replace the thermostat if the inspection gives a negative result. Follow the below steps to change the electronic thermostat properly: 

  • Shut off electric supply to the unit.
  • Remove the upper or the lower access panel and pull away the insulations. 
  • Detach the wires from the electronic thermostats and pull out the bad electronic thermostat. 
  • Install a new thermostat and ensure it fits snuggly against the tank. 
  • Reattach power wires to the thermostat following the wiring diagram. 
  • Replace the insulation and screw the access panels. 
  • Finally, turn the electric supply on to the unit. 

04. Connectors To The Computer Module Gets Burnt Out

Though it’s not usual that damaged connectors to the computer module will be responsible for flashing error code e02, anything can happen. So, it’s worth checking the connectors of the control board. 

How To Fix: 

Visually inspect all the electric wire connectors at the computer module. Repair or replace the wire connectors if they come loose or get burnt out. If you are not electrically inclined, it will be better to call a certified electrician to inspect those connectors professionally. 

05. A Bad Computer Board

And lastly, a bad computer board can also cause your AO Smith Electric Water Heater to throw the error code e02. If the computer board is a problem, the unit will not work properly. 

How To Fix: 

You should deal with electrical wires to replace the computer board. So, I suggest you hire a qualified electrician to change the computer board. You can even call the AO Smith Support Team to do this task for you. 


How do I reset my AO Smith electric water heater?

Just press the red reset button and it will reset your AO Smith Electric Water Heater. You can access the reset button by removing the upper access panel and the insulation.

Why is my AO Smith water heater beeping?

Your AO Smith Water Heater is beeping whenever it senses a problem and warns you by making an audible beep. Besides, scale buildup on the bottom of the tank or the heating element can also cause the water heater to make a noise.

Where is the reset button on AO Smith water heater?

The reset button of the AO Smith Water Heater is located on the upper thermostat. Just unscrew the upper access panel, fold away the insulation, and you can find the reset button right on the upper thermostat.


Measure the selected water temperature by opening the faucet when the water heater pops up the error code e02. Your AO Smith Electric Water Heater flashes this fault code because of a tripped ECO, bad heating elements, and defective thermostats. 

So, follow the troubleshooting steps I mentioned to check these water heater components. If needed, replace them. Finally, reset the water heater to clear the error code e02. 

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