AO Smith Water Heater Keeps Going Into Vacation Mode (Fixed) 

Vacation mode is an energy-saving setting that allows your AO Smith water heater to function at lower temperatures. Most manufacturers set 50°F (10°C) for vacation mode. However, there are times when you’d rather not have your AO Smith water heater vacation mode stay “on.” 

AO Smith water heater keeps going into vacation mode because of carbon buildup on the flame sensor. The flame sensor is a rod that detects low or high wavelength light and converts it to an electrical current. Carbon buildup on the flame sensor interferes with how it interprets the flame. 

I’ll discuss why your AO Smith keeps going into vacation mode, the role of the flame sensor, how you can fix the problem, and other possible causes that may or may not warrant assistance from a professional.

AO smith water heater vacation mode

Why AO Smith Water Heater Keeps Going Into Vacation Mode

If your AO Smith sensor constantly goes into vacation mode, your water heater won’t heat to your desired temperature. Fortunately, this usually has a quick and easy solution. 

But first, let’s talk about the role of the flame sensor (flame rod) in your AO Smith water heater.

The flame sensor is a simple but important component located between the burner and the heat exchanger. If there’s anything wrong with that component, your AO Smith water heater will keep going into vacation mode even when you reset it. 

Let’s go into two of the most common issues with your AO Smith water heater’s flame sensor.

The Flame Sensor Has Carbon Buildup

The flame sensor converts the flame from the burner into an electrical current, which in turn flows into the heat exchanger. 

As the flame burns across the flame rod, carbon builds up over time, as well as dust and other debris. 

Because of the carbon buildup, the flame sensor begins to get the temperature wrong. So, instead of detecting high wavelength light set at higher temperatures, the sensor may mistake it for a low wavelength light (vacation mode). 

In other words, a flame sensor with heavy carbon buildup will keep reading low temperatures and assume that the water heater needs to be in vacation mode. That means even when you turn off vacation mode, the heater will automatically switch back on because the flame sensor keeps detecting the wrong temperature. 

This video explains how a flame sensor works, how it gets dirty, and how you should clean it.

The Flame Sensor’s Insulator Is Cracked

Sometimes, the cause of your AO Smith water heater going into vacation mode isn’t the carbon buildup on the rod. The porcelain part of the flame sensor may be cracked, meaning the flame sensor will not function correctly. 

If this is the problem, you’ll likely need to replace the flame sensor. The flame sensor has a lifespan of 5 years, so if it has worked for that long, it’s probably undergoing normal wear and tear. You can replace the flame sensor yourself, but I strongly recommend getting professional help.

water heater flame sensor

How To Fix an AO Smith Water Heater Going Into Vacation Mode

Since the cause of the water heater going into vacation mode is the flame sensor, the first step you should take is to check if the rod has carbon buildup. To do this, you’ll need to remove the flame sensor and clean it thoroughly.

Here’s how to fix an AO Smith water heater going into vacation mode due to carbon buildup.

  1. Shut off the gas valve and unplug your water heater. You don’t want to handle the flame sensor when it’s hot. Working on a water heater with the gas on is also unsafe. 
  1. Unscrew the access panel. Some models have Torx screws, so have a Torx screwdriver at home in case you need to get into the heater and access the flame sensor.
  1. Remove the burner and pull out the flame rod. 
  1. Use an emery cloth to clean the rod. Rub it until it is shiny. Avoid using sandpaper because it has silica that damages the rod or leaves a silica coating on it. When the flame burns through silica, instead of the easy-to-clean carbon, it will form a glass-like layer on the flame rod which will cause other issues. 
  1. Once the flame sensor is clean, assemble your water heater and restart it. 

If the problem was the carbon buildup, the water heater should function normally now that the flame rod is clean.

To clean your water heater’s flame rod, I suggest getting the LYJFXX Emery Cloth Roll (available on It has four rolls — 6 meters (19.7 feet) each — of assorted grit (150, 240, 320, and 400). The rolls have adjustable lengths and can be used for polishing metal, hardwood, synthetic materials, and much more. They’re packaged in a cardboard box, making them easy to store.

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Causes of Flame Sensor Failure

When your AO Smith water heater keeps going into vacation mode, the problem is usually the carbon buildup on the rod. This can usually be addressed by cleaning your flame sensor at least once a year. 

However, if you find an excessive amount of carbon buildup that an annual cleaning can’t address, there may be a deeper issue.

The heavy carbon buildup on your AO Smith water heater’s flame sensor can be caused by one or more of the following.

  • The water heater may not be burning the right amount of fuel. In that case, you need to perform a combustion analysis of your water heater.
  • The gas may be leaking due to a faulty gas valve. You may need to replace the valve. Otherwise, carbon will keep accumulating on the flame rod. If your appliance is at least ten years old, getting a new heater may be the best idea.
  • The air around the water heater is filled with contaminants. If the room is dusty or close to your workshop, that may cause impurities to collect on the flame rod. Therefore, you must find ways to keep the air around the water heater as free of contaminants as possible. Failing that, you may need to move your heater to another location. 

Aside from excess carbon buildup, you may also want to consider the possibility of a cracked insulator or defective sensor. A short may have developed in the electrical component, stopping communication with the control board. In both of these cases, professional help is necessary.

fixing the flame sensor on AO smith water heater


Fixing an AO Smith water heater that goes into vacation mode is straightforward. However, if you’re not familiar with the water heater and the wiring process, it’s safer to contact a professional who can fix the problem. You can prevent some of these issues by conducting annual maintenance, which usually includes cleaning the flame sensor.