Why Is My AO Smith Water Heater Blinking Green Light?

What I am going to break down: 

  • Why does the AO Smith Water Heater blinking green light and what does it mean?
  • A complete chart of AO Smith Water Heater Flashing Codes
  • The corrective actions you should take to stop the blinking light

So, let’s dive into this article. 

Table of Contents

Why Is My AO Smith Water Heater Blinking Green Light?

Blinking green light (or the red light) on AO Smith water heater actually indicates the status of the electric thermostat. If the status light blinks green continuously, be assured that your water heater is running at its tip-top condition. 

In short, the green LED on the AO Smith Water Heater will signal normal operation. If the green light blinks 2 times per two seconds repeatedly, understand power is applied to the upper heating element. 

On the other hand, if the green light flashes at a faster rate like 4 times per second, it indicates the power is applied to the lower heating element. 

Now, one question may spin around your head from curiosity is- Do I need to take any corrective action if the water heater is blinking a green light? 

Luckily, No. Then, when should I take the corrective actions in regards to blinking status light? 

Well, you should take action if you notice there is no light or the status light flashing red. The next chapter will give the answer with details. 

AO Smith Water Heater Diagnostic Code Chart

You already know you don’t need to do anything if the status light blinks green. But what do you do if there is no status light or the status light blinking red? To know what you should do, I suggest you read the rest of this article. 

01. No Light

The status light will never blink due to these two reasons: 

  • Control board gets no electric power
  • The diagnostic LED Light may blow or burn out. 

What To Do: 

  • Inspect the fuses or circuit breaker for the trip. If they get tripped, replace them.
  • Replace the electronic thermostat if the LED light gets burnt out. 

02. Status Light Flashing Red 1 Times

1 Blinking Red Flash indicates a dry-fire. But, what is dry-fire? If you power on your water heater without filling the tank with water, it will burn or damage the heating element. And this is known as dry-fire. 

What To Do: 

First, turn the electric supply off to the unit at the circuit breaker. Next, fill the tank with water by opening the cold water supply valve. Once you fill the tank, turn the electric power back to your water heater. If still there is any problem with the unit, contact a qualified plumber. 

03. Status Light Flashing Red 2 Times

Two consecutive red flashes per second means the water temperature exceeds the high limit. In this case, you can find the water heater throws an error code ‘E02’ at the same time beside the two red flashes. 

What To Do: 

What you need to do is- turn the power off to the unit. Then, remove the upper access panel, fold away the insulation, and get the red reset button. Next, press the button to reset the unit. Lastly, turn the power back to the unit. If the problem returns, you should call a technician. 

Anyway, I already covered an in-depth guide on AO Smith Water Heater Code E02. I discussed what troubleshooting steps you should take to clear the error code ‘E02’. 

04. Status Light Flashing Red 3 Times

If the status light blinks red 3 times, I bet there is a problem with the upper thermistor sensor. The upper thermistor is a part of the electronic thermostat. When it’s at fault, it will cause the status light to flash 3 times per second. 

What To Do: 

Just turn the power off to your water heater. Then, follow the instructions on the manual to replace the electronic thermostat. If you are not mechanically inclined, call a certified plumber to do this for you. Finally, turn the electric supply on to your unit once you change the ET. 

05. Status Light Flashing Red 4 Times

Flashing red status light for 4 times per second on AO Smith Water Heater indicates an upper element circuit failure. Keep in mind; the lower element will still be operable. 

What To Do: 

1. Ensure you turn the electric power off to your water heater at the circuit breaker. 

2. Measure the resistance of the upper element. Follow the below step-by-step procedure to check the upper element circuit electrically: 

  • Remove the upper access panel by unscrewing it with a flat head screwdriver. 
  • Fold away the insulation. 
  • Get a multimeter and place the both leads of it between the two screw terminals on the upper heating element. 
  • The resistance of a healthy upper heating element should be between 5 to 25 Ohms. If the reading goes out of the range, replace the upper heating element. 

3. Inspect the wiring at the upper heating element and the electronic thermostat. If the problem still persists, replace the ET (electronic thermostat). 

4. Finally, turn the electric power on at the breaker. 

06. Status Light Flashing Red 5 Times

The red flashing code ‘5 consecutive blinks per second’ indicates the opposite problem of ‘status light flashing 4 times’. In simple words, the status light will blink red 5 times when the lower element circuit gets defective. 

What To Do: 

Just ensure you shut the electric supply off to the unit. Then, remove the lower access panel and pull out the insulation gently. 

Now, get a multimeter and use it to measure the resistance of the lower element. A functional element will give a reading between 5 to 25 Ohms. Otherwise, you must replace it. 

Then, check the wiring and the electronic thermostat. If the flashing code returns, replace the lower electronic thermostat as well. 

07. Status Light Flashing Red 6 Times

Does the AO Smith water heater blinking red 6 times per second? Then, understand there is a problem with the electronic thermostat. Basically, the electronic thermostat gets bad if its internal processor is at fault. 

What To Do: 

Locate the circuit breaker of your water heater and flip it to turn off the electric supply to your water heater. Then, turn the power back to the unit again. If the error still persists, you must replace the electronic thermostat to fix this issue. 

08. Status Light Flashing Red 7 Times

If the lower thermistor sensor gets defective, the status light of your AO Smith Water Heater will blink red 7 times. 

What To Do: 

First off, flip the circuit breaker of your water heater to the off position. Then, inspect the electronic thermostat wiring for damage. Next, change the lower thermistor sensor. Afterward, turn on the electric supply to the unit again. 


Don’t drive crazy if you find the status light of your AO Smith Water Heater blinking green as it signals normal operation. 

However, you may go nuts if you observe the status light blinking red. But this is not going to happen anymore because I broke down the meaning of the red flashing codes. 

Also, I discussed the correction actions you need to take to decode or solve the flashing codes. 

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