AO Smith Water Heater Not Heating

AO Smith Water Heater Not Heating [5 Easy Solutions]

The AO Smith Water Heater is not heating due to several reasons. For example, if it’s an electric water heater, it won’t heat if the upper heating element gets burnt out or faulty. 

Tripper ECO switches or broken thermostats are other culprits that prevent the unit from heating. 

And this troubleshooting guide will break down everything to bring your water heater back into the operating conditions. So, let’s dive in.

Table of Contents

Why Is My AO Smith Water Heater Not Heating?

Your AO Smith Electric Water Heater won’t heat due to the following reasons: 

  • Unit gets no electric power
  • Burn out upper heating element 
  • ECO (energy cut-off) switch gets tripped
  • Inlet and outlet connections get reversed
  • Upper thermostat gets broken 

01. Unit Gets No Electric Power

Electric issues are common with new installations. It generally occurs if there is a problem with home electrical wirings or circuit breakers. Your water heater won’t heat if the unit doesn’t get any power. 

How To Fix: 

It is impossible to say the home’s electrical wirings are at fault without testing them electrically. You need a non-contact circuit tester to inspect the wirings. Once you get one, it’s time to find the water heater circuit breaker and set it to the off position. 

Then, remove the junction cover from the electrical junction box, which you can find on top of the water heater. 

Next, identify two power wires. Black-black or black-red are the power wires. And the color of ground wirings is green or copper wiring. 

What you should do next is- turn on the circuit breaker and use the non-contact circuit tester to test the two power wires. 

If your AO Smith Water Heater doesn’t get any power, you should call a certified electrician to fix the electrical issues. So, turn off the circuit breaker, replace the junction cover, and call an electrician.  

02. Burn Out Upper Heating Element

If your water heater is getting electrical power, you must check the upper heating element next. Actually, the burn-out upper heating element is the main culprit that prevents your water heater from heating. 

The upper heating element gets burnt out or faulty due to age or electrical issues. For new installations, dry fire is the common reason for a fried heating element. 

But, what is dry-fired? An upper heating element that gets burnt out due to turning the power on before filling the water tank. It’s known as dry-fire. In this case, you must replace the burn-out heating element. Otherwise, your water heater will never heat the water. 

How To Fix: 

Don’t jump the gun on replacing the upper heating element before checking it electrically. To test the heating element, get a multimeter. 

Second, turn the power off at the circuit breaker. Then, remove the upper access panel by using a flat head screwdriver and fold away the insulation. 

Thirdly, use the non-contact circuit tester to ensure there is no electrical power on the top two screws of the upper thermostat. 

Fourthly, remove the two power wires from the heating element. Now, place the multimeter between two screw terminals on the heating element. A healthy heating element should give a reading between 5 to 25 Ohms. 

If the resistance of the heating element goes out of range, you should replace the upper heating element. I recommend you watch this tutorial that will help you in changing the heating element: 

03. Energy Cut-off (ECO) Switch Gets Tripped

The Energy Cut-off Switch is a safety feature of a water heater. It cuts the electric power to the heating elements so that they fail to heat the water. Basically, this energy cut-off switch gets tripped when the sensor senses too hot water temperature. And your water heater doesn’t heat the water with a tripped Energy Cut-off or reset button. 

How To Fix: 

Resetting the energy cut-off or reset button can be a simple fix to this problem. To reset the water heater, what you need to do is- 

  • Turn the electric supply off to your water heater at the circuit breaker.
  • Unscrew the upper access panel. 
  • Remove the insulation to access the red reset button, which you can find on the thermostat. 
  • Press down the reset button and you will hear a click, which indicates you reset it. 
  • Put both the insulation and the upper access panel back into their places. 
  • Finally, turn on the electric power to your unit. 

Note: I recommend you hire a certified plumber to figure out what causes the overheating issue. 

04. Inlet and Outlet Connections Get Reversed

This issue typically occurs with new installations. If you mistakenly connect the inlet connections to the outlet one, you will get no hot water. 

How To Fix: 

The solution to this problem is simple. Just ensure you correctly make the inlet and outlet connections. I recommend you install the water heater by a professional to avoid this issue. 

05. Broken Upper Thermostat

Your AO Smith Water Heater will heat the water intermittently if the thermostat gets broken. The main work of the upper thermostat is to control at what temperature the heating element will heat the water. If it gets broken, the upper heating element will no longer work. In the worst, the lower thermostat will also not work due to a bad upper thermostat. 

How To Fix: 

First off, shut off the electric power to the unit at the circuit breaker. Secondly, remove the upper access panel and fold away the insulation to access the upper thermostat. Then, visually inspect the upper thermostat for damage. 

If it gets damaged, you should replace it. Just pull the wires from the thermostat and slide it out. Now, install the new thermostat and connect the wires correctly. You can see the following video to replace the upper thermostat: 

On the other hand, if you have an AO Smith Gas Water Heater, the unit won’t heat due to the following reasons: 

  • Cross plumbing between the cold water lines and hot water lines
  • The gas supply valve is not fully open
  • Size the gas line improperly 
  • Insufficient gas supply pressure 
  • You may set the temperature too low

I broke down each of them in this article on AO Smith Gas Water Heater Troubleshooting. So, check that article and solve the not-heating issue. 


Nothing is more frustrating than a non-functional water heater in the ice-cold days of winter. If your AO Smith Water Heater is not heating, you can hardly do your household chores like washing dishes or taking a bath. 

Fortunately, I discussed everything and mentioned the troubleshooting steps you should follow to solve the no-heating problem. So, follow the guideline and fix the issue. 

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