AO Smith Water Heater Thermostat Problems

Warm water can be delightful on very cold days. But when the water from your AO Smith water heater is not hot or too hot, there are problems with the thermostat.

Your AO Smith thermostat malfunction may be related to a faulty thermostat, a bad reset button, and power problems. Your water heater may not release enough water or release water that’s either not hot or too hot. Replace your wiring, thermostat, reset button, or heating element to fix the problem.

AO Smith water heater thermostat

Before you fix any components or replace the entire thermostat, you need to test and identify the issue, as the appropriate remedial action will depend on what went wrong. This article examines each of these problems with attendant solutions.

1. Power Supply Problems

No device will work without a power supply. If your AO Smith thermostat is not working, there may be an interruption to the power supply and a loss of function. 

The thermostat may not activate the heating element or regulate the temperature when it exceeds the thermostat limits. The heater may warm up the water, but without the regulatory function of the thermostat, the water will become too hot. 

How To Fix

Power problems may be due to a faulty thermostat or bad or damaged wiring. Power travels from the electric source in your house to your heater and moves to other components, including the thermostat. If power isn’t getting to the heater, the house fuse or circuit breaker may be faulty

However, if power isn’t getting to the thermostat, open the thermostat panels, check for loose or damaged wiring, and repair where necessary. If the internal wiring in the thermostat is in good condition, your thermostat may be bad.

AO Smith Water Heater

2. Faulty Thermostat

A faulty thermostat will not function effectively or may not function at all. The thermostat works as a switch to activate or deactivate the heating element in the water heater based on the temperature of the water.

Your AO Smith electric water heater thermostat is an assembly of two thermostats – the upper and lower thermostat. The upper thermostat activates the heating element at the top of the water tank, while the lower thermostat activates the heating element at the bottom of the tank. 

If any of these parts malfunction, it will affect the overall function of the water heater. The usual problem is that your AO Smith does not heat water or may produce too hot water. However, in some cases, your water heater may take a longer time to heat water.

How To Fix

A bad thermostat needs replacement. But before you conclude that your thermostat is faulty, you’ll have to test it for electrical continuity. To test your thermostat, get a Torx or an appropriate screwdriver and a multimeter and follow the steps below.

 holds a thermostat water heater
  1. Turn the heater off. Turn off the power to the water heater.
  1. Open the thermostat. Use a screwdriver to open the upper and lower thermostat access panels. Remove insulation for easier access.
  1. Disconnect the thermostat. Isolate the thermostat from the entire unit by detaching the power wires connected to the thermostat.
  1. Connect your multimeter. Set it to its lowest setting and connect one probe to the left-side terminal beside the reset button. 
  1. Test the upper thermostat. Adjust the thermostat to the highest temperature. Connect the other multimeter probe to the left-side terminal. Then, adjust the temperature to the lowest setting and connect the probe to the right-side terminal. Note the readings. 
  1. Test the lower thermostat. Turn the lower thermostat to the minimum value. Connect one end of the meter probe to one terminal and the other end to the other terminal. Note the readings

The multimeter reading indicates whether the thermostat is faulty or not. A zero (0) multimeter reading means that the thermostat is in good condition. If the thermostat is okay, you may need to reset the thermostat using the reset button. Otherwise, the thermostat is defective and needs replacement.

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3. Damaged Reset Button

A functioning AO Smith water heater should release hot water that doesn’t exceed the upper-temperature limit of your thermostat. So, if you’re not getting hot water or water that’s too hot, the thermostat may be stuck in the heating or cooling mode.

Asides from getting stuck, your AO Smith water heater thermostat may start tripping on and off. Resetting your water heater thermostat can help restore your heater to normal function. However, this becomes impossible when the reset button is damaged.

How To Fix

A damaged reset button needs replacement. While replacing a button may sound simple, I recommend using a professional for fixing electrical installations unless you’re an expert. If you attempt DIY tips, you may damage the device.

4. Bad Heating Element

If the heating element in your water heater is broken, it could damage your thermostat. The heating element is a device in the water heater that converts electrical energy to heat energy. 

The heating element is a resistor that heats up when electricity flows through it. The heat transfers to the water, increasing the water temperature until it reaches the thermostat limit. Heating elements can go bad due to certain factors, such as

  • Sudden power surge
  • Mineral elements corrosion
  • Bad wiring

When the heating element is bad, the water may take a long time to become hot, may not produce enough water, or may discharge hot water too quickly. 

Details of a disassembled water heater. Anode, heating element, temperature sensor, gaskets, flange

How To Fix

You should test the heating element before you decide to replace it. To test your heating element, you need to measure the electrical resistance. Here’s how. 

  1. Turn the power off. This is a standard safety protocol for repairing electrical installations. 
  1. Measure resistance. Adjust the meter to its lowest setting and connect the probes to the terminals of the heating elements. Note the resistance readings.
  1. Check for shorts. To test for shorts, connect the probes to one terminal and the other to the covering of the heating element. Note the readings.

Normal resistance readings range from 9 to 12 ohms. Low or very high readings indicate a bad heating element. When testing for shorts, an infinite reading indicates no continuity to the ground. Any reading means there’s a short, and the heating element is bad.


The thermostat is central to the functioning of your AO Smith water heater. The water heater can malfunction when the thermostat develops problems. Power problems, a bad reset button, a bad heating element, or even internal damage can contribute to thermostat function. After testing with a multimeter, you may need to replace or fix damaged parts.