AO Smith water heater troubleshooting guide

ao smith water heater troubleshooting

AO Smith water heaters are some of the most popular on the market, and for a good reason. They’re reliable, efficient, and easy to use – perfect for any home.

However, like any other appliance, problems can sometimes crop up with an AO Smith water heater. This AO smith water heater troubleshooting guide will walk you through some common issues and how to fix them. 

AO Smith water heater troubleshooting

If you are having problems with your AO Smith water heater, there are a few things that you can do to try and fix the problem.

1. Leaking or Smelly Water

If you notice bad odors from your water heater, one of the most likely causes is a leak in the water line. To check for leaks, turn off the power to the unit and locate the cold and outgoing hot water lines. Try to identify where the leak is located with your hand. You may need to call a technician if you can’t find the leak.

Another common cause of leakage and bad odors is sediment buildup in the water tank. This can happen if your unit isn’t regularly serviced or has an issue with your water lines. If you notice sediment buildup in your water tank, it is important to have it cleaned by a technician.

If you are experiencing water leakage and bad odors, another likely cause is clogged filters. To check for clogged filters, turn off the power to your unit and check the filter. Cleaning and servicing your unit may be necessary if clogged filters are present.

Leaking or Smelly Water

2. Pilot Light Issues

If your AO Smith water heater is having problems with the pilot light, you can do a few things to troubleshoot the issue.

First, ensure that the gas line is properly connected to the water heater and that the connection is tight. If the connection is loose, the pilot light may not stay lit.

Next, check to see if anything is blocking the gas line or gas feed from reaching the water heater. If something is blocking the gas line, it will prevent it from lighting up when it reaches the water heater.

And follow the below steps:

  • A perpendicular gas valve indicates that the feed has been shut off.
  • Align the gas valve with the gas line.
  • A dirty pilot assembly could also prevent your pilot burner from lighting. The owner’s manual will provide instructions on how to clean the pilot assembly.
  • Relight the pilot according to the manual’s instructions.

A pilot light malfunction could also be caused by:

  • A wire disconnected from the spark ignitor
  • A thermocouple malfunction
  • A broken electrode
  • Melted insulation

If all the steps fail to fix the problem, you may need to replace the pilot light assembly. Hence, a qualified technician is required.

 3. Water Temperature

The water in your AO Smith water heater is working hard to keep you warm and comfortable. However, it may be time to troubleshoot the issue if the water heater starts to struggle. If you still have trouble, don’t hesitate to contact AO Smith for support. We’re here to help!

1. The first step in troubleshooting a water heater is checking the water temperature. If the water is too hot or cold, it will affect the overall performance of the appliance.

2. To check the water temperature, open a faucet in the room where the water heater is located and wait two minutes for the temperature to equilibrate. Record the reading on a thermometer. If it’s below 60 degrees Fahrenheit or above 120 degrees Fahrenheit, adjust the thermostat on your AO Smith water heater accordingly.

3. Another possible solution could be raising the thermostat if the hot water from a faucet is too hot. You can lower the temperature by adjusting the heater’s control knob if that’s the problem.

4. Check that you are turning the knob in the right direction because if you turn it incorrectly, the water will become even hotter.

Additionally, if you adjust your settings and still feel lukewarm water when running your hand under the faucet, replacing the tank is necessary due to an undersized tank.

Water Temperature

4. Sizzling or Rumbling Sounds

If you’re noticing a high-pitched sizzling or rumbling noise from your AO Smith water heater, there’s a good chance it’s time for a replacement. 

1. Bad Water Heater Gasket

2. Inadequate Venting

3. Damaged Heating Element

4. Water Leak

It is also possible that sediment has built up inside the tank of an A.O. Smith hot water heater that makes sizzling or rumbling sounds. To fix this problem:

  1. Connect a hose to the drain valve and lead it outside.
  2. Drain and flush the tank while turning off the pilot light and gas feed line.
  3. While draining and flushing the tank, close the hot water valve that feeds the house.
  4. Flush the tank with clean cold water until the water at the end of the hose runs clear.
  5. Remove the hose and close the drain valve to fill the tank.
  6. Light the pilot and restore the gas supply.

5. No Hot Water

One of the first things you should do if you are experiencing a problem with your hot water is to check the thermostat. If the thermostat is not set properly, it could block the water heater from heating up, leading to a lack of hot water.

To check the thermostat, unplug the water heater. Then, use a thermometer to measure the water temperature inside the water heater tank.

Compare this temperature to the manufacturer’s recommended temperature range on the thermostat. If the temperature is outside this range, adjust the thermostat setting accordingly.

Another common cause of a lack of hot water leaks. Check all faucets and pipes for leaks, including around your water heater. If you find any leaks, fixing them can help you address them quickly and cheaply.

If none of these steps help solve your problem, it may be time to clean or replace your water filters. Filters can become clogged over time, leading to a lack of hot water. Clean your filters with a filter cleaner, then replace them if necessary.

No Hot Water

6. Dripping Water

If you are having trouble with your AO Smith dripping water heater, follow these simple steps to diagnose and fix the issue.

Step 1: Verify that the water is flowing correctly

First, ensure that the water flows correctly from the tank to the faucet. If there are any blockages, you will need to clear them before proceeding.

Step 2: Check for a clogged drain

If the water is not flowing and there are no blockages, you may need to check for a clogged drain.

To do this, turn off the water at both the faucet and the tank and use a broom to sweep up any debris that may have accumulated in the drain. If debris is still blocking the drain, you need to call an expert to clean it.

Step 3: Test for a defective pressure switch

If all these steps fail to fix the issue, you may need to replace the pressure switch.

To do this, you will need to access the pressure switch. Once you have accessed the switch, test it for continuity by touching each wire with a multimeter. You will need to replace the switch if there is no continuity between the wires.

7. Too Hot Water in the water tank

When the water in your AO Smith hot water tank starts to feel too hot, you can do a few things to try and fix the issue.

If the water in your tank is simply too hot, you can try turning down the thermostat. This will reduce the heat in the tank and make the water cooler. If that doesn’t work, you may need to call a professional to come and fix your water heater.

8. Compressor Stop Operating

If you’re having trouble with your AO Smith water heater, it’s probably because the compressor has stopped operating. 

To start, it’s important to determine if the compressor is working. If you can hear the compressor running, then it’s likely operational. However, if you can’t hear the compressor running or it’s making strange noises, it’s likely not operating properly and needs to be repaired.

To troubleshoot the compressor, start by checking the fuse box for any blown fuses. If there are no blown fuses, check for power at the motor. If power is present at the motor but no sound comes from the compressor, the problem may be with the belt or pulley. If there is looseness or wear on the belt or pulley, replacement may be necessary.

9. Insufficient/Slow Hot Water

If you are experiencing low or inadequate hot water from your AO Smith water heater, you can do a few things to troubleshoot the issue.

First, ensure that the water heater is properly connected to the water supply and is working properly. If the water heater is not connected properly, it will not be able to produce enough hot water.

Second, check the flue pipe connection on the water heater for obstructions. Any obstructions in the pipe will restrict heat from reaching the water heater and cause it to operate slowly or not at all.

Finally, if all of these tests reveal no problems with the water heater, it may be necessary to replace it.

10. Temperature Drip

First, check to see if the water is hot enough. Turn the thermostat or check the gas supply if it isn’t hot enough. Next, try turning on and off the power to the unit several times. This can sometimes reset the thermostat. 

A.O Smith water heater troubleshooting lights

A.O Smith water heater troubleshooting lights

If the “heating” and “open” flashing lights are on, ignition or flame failure might occur.

Some water heaters ignite gas with an igniter. If the igniter fails, the burner won’t light. Check that the igniter gets voltage before determining if it’s defective. Replace the igniter if it receives voltage but does not glow.

The pilot ignites the water heater’s gas burner. If the pilot does not light, the water heater will not heat. Using a stiff brush and compressed air, clean the restricted pilot. If you can’t clean the pilot, replace it.

A.O Smith water heater gas control valve troubleshooting

If your A.O. Smith water heater does not heat water, there is a good chance your gas control valve is not working properly. Follow these steps to troubleshoot the issue:

1. Check the flame sensor and pilot light to ensure they work. If they are not, the gas control valve may be defective.

2. Check the gas line connected to the valve. Be sure it is tight and free from any leaks. If the line is loose, debris can accumulate inside the valve, causing it to malfunction.

3. Test the gas flow by turning on the gas supply and trying to turn on the water heater using the knob.

If the valve does not flow the gas, there may be a blockage in the line between the valve and the gas supply. Remove any obstructions and try again.

4. If all of these tests fail to solve the problem, you may need to replace the gas control valve.

A.O Smith gas water heater troubleshooting burner screen

A.O Smith gas water heater troubleshooting burner screen

If the burner is not working, the worn-out thermocouple has likely the main cause. To fix this, you must remove the burner screen and clean it. Once it is clean, reattach the screen and reinstall the burner. If the problem persists, you may need to replace the burner.

A.O Smith water heater error codes

If you are experiencing problems with your A.O. Smith water heater, there are a few things you can do to try and diagnose the problem. Here are some common error codes and what they mean.

Error codesProblem
03 (031), One-timeDipswitch settings are incorrect.
10 (101), Five timesError code “991” warning.
11 (111), Three timesFailure of the ignition.
12, 121, Three timesLoss of flame.
31, 311, Two timesFailure of the outlet thermistor.
32, 321, Two timesFailure of the inlet thermistor.
331, Two timesFailure of the mixing thermistor.
341, Two timesFailure of the exhaust thermistor.
39, 391, Two timesThe air-fuel ratio rod – AFR – has a problem.
441, Two timesFlow sensor problem.
51, 55, 510, 551, Six timesA gas solenoid valve is abnormal.
61, 611, Four timesFaulty fan motor.
651, Four timesFault with the flow adjustment valve.
661, Four timesFaulty bypass valve (only on model 540).
70, 701, One-timeComputer board problem.
711, One timeFailure of the gas solenoid valve drive circuit.
72, 721, Six timesDetection of a false flame.
74, 741, 751Water heater and remote controller miscommunicate.
761Easy-Link System miscommunication.
99, 991, Five timesGas combustion is improper.


If you are experiencing problems with your AO Smith water heater, don’t hesitate to call professionals. They have the experience and knowledge to help you figure out the problem and get your water heater up and running as quickly as possible.

We hope we have answered your question about how to repair an A.O. Smith gas water heater. If you have additional questions, please let us know. We’re here to help!


Why is my A.O. Smith water heater not getting hot?

If your A.O. Smith water heater is not getting hot, there may be a problem with the water heater’s valve or thermostat. In some cases, the water heater may also need to be replaced. To check if the water heater is defective, follow these steps:
– The thermostat may be set too low.
– Check that the pilot light is lit.
– Make sure that there is no blockage in the vent pipe.
– Make sure the gas valve is turned on.
– If you have an electric stove, make sure it’s plugged in.

What trips the reset button on a hot water heater?

A trip to the reset button on a water heater is when there is a loose electrical connection within your water heater’s system. 

How do I know if my hot water heater element is bad?

If your hot water heater element has been running for a long period of time, then it may be damaged.
To check whether your hot water heater element is working properly, turn off the power supply at the breaker box, wait about 10 minutes, and test the element using a multimeter.
No reading or a maximum reading indicates a bad element. As elements have some resistance, a reading of 10-16 ohms is normal, with higher ohm readings for 3,500-watt elements and lower readings for 5,500-watt elements.

How long do you hold the reset button on a hot water heater?

The reset button on an AO Smith water heater should be held until you hear a click. If this does not work, the reset button may need to be broken off and replaced.

Where is the A.O Smith Water Heater Reset Button Located?

If you are having trouble with your A.O. Smith water heater, the reset button may be on the side of the unit. The reset button is located below the top panel cover on the side of the water heater.

How to Reset Your A.O Smith Water Heater?

If your water heater has stopped working properly, you should call for help from a professional plumber.
1. You first need to turn off the power supply at the breaker box. Then, you must turn off all electrical connections from the unit that is labeled with a water heater.
2. Check your hot water heater. You can remove the top panel cover by removing the screws. The reset button is inside the panel.
3. Press the reset button to reset the device. You should hear a clicking sound when the water heater is reset.
4. Flip the breaker switch to turn on the electrical panel.