AO Smith Water Heater Blinks 3 Times (4 Easy Fixes)

Your heart may skip a beat when you notice your AO Smith water heater blink three times. When this happens, the first question that may ring in your mind is, “Is my water heater about to blow up?” While a blinking light indicates a problem, it’s not always a cause for alarm.

When an AO Smith water heater blinks three times, it may be due to a pressure switch that has failed to close, an exhaust vent being closed, a faulty gas valve, or blower issues. Solutions include replacing the blower assembly and pressure switch.

AO Smith water heater blinks three times

In the rest of this article, I’ll discuss the causes of the AO Smith 3 flash code. I’ll also cover how to fix these issues and get your water heater back to normalcy. Let’s get started!

1. A Pressure Switch That Has Failed To Close

Your AO Smith water heater has a pressure relief valve that relieves excessive tank pressure. The pressure switch is a fail-safe mechanism that turns off the gas to the burner if tank pressure gets too high.

If the pressure switch is not working, the AO Smith water heater will blink three times. In most cases, the blinks indicate that the water heater’s fan is not working.

The fan is responsible for drawing air into the combustion chamber. If the fan is not working, the water heater will overheat and shut down.

pressure switch

A pressure switch may fail to close due to the following:

  • Lack of continuity between its terminals.
  • A faulty pressure switch.

How To Fix

You can fix this problem by checking the continuity between the pressure switch terminals or replacing the pressure switch. 

To check for continuity between the terminals:

  1. Disconnect the tube attached to the pressure switch.
  2. Connect a digital manometer to the pressure switch.
  3. Turn on the water heater and wait for some time until the blower attains full speed.
  4. Note the pressure readings. The air pressure reading should be more or equal to the activation rate for the contacts to close. If this is the case, then the problem is a faulty pressure switch. In this case, you’ll have to replace the pressure switch.

2. A Closed Exhaust Vent

An AO Smith water heater exhaust vent allows the hot exhaust gasses to escape from the water heater. If the exhaust vent is closed, the hot gasses will build up and eventually cause the water heater to shut down.

The three flash code, in this case, notifies you that the hot exhaust gasses are building up in the water heater, and you should take the necessary action to resolve the problem.

How To Fix

You can fix this problem by opening the exhaust vent. Once you’ve done that, restart the water heater and wait some time to see if the problem persists.

If the above fix fails, replace the fan and the exhaust vent. However, you should also consider the heater’s age. Replacing the exhaust vent is not cost-effective if you’ve been using the heater for more than ten years. In this case, you should consider installing a new water heater system.

3. A Faulty Gas Valve

If the AO Smith water heater’s gas valve is faulty, it may not be able to supply enough gas to the burner. This will affect the heater’s heating efficiency since the burner will not be able to generate enough heat due to insufficient gas.

water heater's gas valve

A faulty gas valve is one of the most common reasons for the three flash codes. In most cases, a defective gas valve is caused by the following:

  • A break in the wire that connects the gas valve to the control board.
  • A loose connection between the gas valve and the control board.

How To Fix

Inspect the wire connecting the gas valve to the control board. 

  1. If the wire is broken, replace it with a new one.
  2. If the wire is not broken, check the connection between the gas valve and the control board. If the connection is loose, tighten it.
  3. If you still can’t fix the problem, replace the gas valve.

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4. Blower Issues

The blower provides air to the combustion chamber.

A long blower vent run reduces the cubic feet of air moved per minute over time. When the cubic feet of air moved per minute to the fan decreases, the fan’s ability to pull the pressure switch is reduced. The consequence is a pressure switch that doesn’t close and the water heater shutting down.

long blower vent

How To Fix

If your blower vent run is too long, you can try one of the following solutions:

  • Use a bigger blower.
  • Reduce the length of the vent run.
  • Install an inline booster fan to help move air through the vent run.


An AO Smith water heater that blinks three times indicates a faulty issue with the heater’s operation. When this happens, your water heater is at risk of bursting or offering you poor heating efficiency. Therefore, you should identify the cause and fix it as soon as possible.

You should check to ensure the exhaust vent is not blocked and that the gas valve provides enough gas. If the problem persists, you may need to replace the blower or install a new AO Smith water heater system.