AO Smith Water Heater Only Warm Water

Has a chilly shower greeted you on more mornings than you’d care to admit? If so, it’s likely that your AO Smith water heater isn’t heating water to the temperature you’ve set… or maybe even at all.

When your AO Smith water heater isn’t hot enough, the cause is likely to be connected to sediment build-up, a dip fracture, damaged heating elements, or a thermostat malfunction. Solutions include flushing your water tank, replacing the broken heating elements, and resetting your thermostat. 

But don’t worry! In most cases, you’ll find this is an easy fix. The following are a few common reasons why your AO Smith water heater is not producing enough hot water and how to solve this problem.

AO Smith water heater only warm water

1. Damaged Heating Elements

Damaged heating elements are the most common causes of your AO water heater not being hot enough. Such elements are a pilot light, the gas valve, and a thermocouple. 

The pilot light is responsible for creating a flame to ignite your gas water heater. If the flame doesn’t ignite, your AO Smith water heater won’t produce hot water. A common cause for a pilot light failing to ignite is carbon deposits, which prevent it from functioning correctly. 

The gas valve is responsible for lighting the burner, and the burner must be lit to heat up the water. You should check if the ignition source is working properly and the gas valve has pressure. If it has pressure, you may need to replace the gas valve.

Your AO Smith water heater’s thermocouple will turn off the gas valve if it doesn’t detect a flame in the pilot light. When this happens, it won’t allow the gas to reach the pilot light correctly.

How To Fix

Faulty heating elements are a prevalent issue and easy to replace, but they can get expensive if you buy one at the store. If you have any knowledge of plumbing, then this is something you should be able to do yourself. 

If the heating elements are not producing enough heat, they will need to be replaced. Always replace with an exact replacement or an equivalent. 

Before replacing the pilot light, you could try cleaning it. You can do this with compressed air or a stiff brush if it looks congested. If you can’t clean the pilot, you should replace it. 

The same goes for the gas valve and thermocouple – if they are not operating correctly, you will need to seek a replacement.

These repairs can be addressed by anyone who has basic skills in DIY projects. Below are three videos to assist you in replacing your AO Smith water heater’s damaged heating elements:

Pilot light:

Gas valve:


2. Sediment Build-Up in the Tank

Over time, minerals can accumulate at the bottom of the water tank due to increased operating temperatures. As the build-up grows, the heat transfer between the gas burner and water inside the tank is reduced.

Hard water is rich in minerals, and if you live in a hard water area, the water heater can have a mineral build-up. 

Sediment build-up in the water tank can cause your water heater not to heat up correctly. The sediment accumulation will also likely cause your heater to turn on and off or only give you lukewarm water. 

sediment build-up in the tank

How To Fix

You can fix a sediment build-up issue in your hot water tank by having it flushed at least once a year. This will help remove the mineral build-up. 

If you live in an area with hard water, you might consider installing a whole-house water softening system to keep the mineral build-up at bay.   

Here is a video demonstrating how you can flush your AO Smith water heater:

3. The Dip Tube Is Fractured

If your AO Smith water heater is not hot enough or seems to take longer to heat up, it could be due to a broken dip tube. The dip tube is an essential feature in your AO Smith water heater because it helps distribute incoming cold water throughout the tank’s interior. 

It also brings hot gasses from an external combustion device into the tank to distribute them through its sides and bottom. 

How To Fix

The dip tube is located at the bottom of your water heater. If you have any concerns about whether it is visibly damaged or cracked, then follow these steps:

  1. Remove some insulation in the area around the tube. 
  2. Inspect the tube closely for fractures or chipping in its surface. Use a flashlight for this task if you cannot see clearly through all of the material. 
  3. If there are any cracks in the tube, replacing it will solve most issues with your AO Smith water heater not being hot enough. 

Here is a video to help you replace the dip tube:

4. Thermostat Malfunction

A thermostat is a device that controls and regulates the water temperature in your AO Smith water heater. It is located on the top of your tank and usually has a dial to set it to your desired setting. 

If you have an older model heater, there may be no dial or dials on the top; instead, it could be inside or underneath the unit.

How To Fix

If your hot water runs cold when you turn it on, your thermostat may have malfunctioned. Here’s how to test your thermostat:

  1. Disconnect the power to your water heater completely. 
  2. Don’t touch the water heater for 30 seconds to ensure that there is no remaining electrical charge. 
  3. Using some pliers or a screwdriver, pry open the heater’s panel or unscrew it. 
  4. Use a screwdriver to adjust the upper thermostat maximum temperature setting to the right. 
  5. Use a meter by placing a probe on terminal 1 (directly above terminal 2) and on the bottom left terminal. 
  6. The reading should now be 0.
  7. If you don’t get a reading, the water heater is likely faulty.

If you find that your thermostat is defective, you’ll need to seek a replacement.

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5. Wear and Tear

Wear and Tear is an expected outcome of owning any water heater. Continuing faults and long-time usage will degrade your AO Smith water heater. 

With every use, sediment builds up inside the tank, restricting its ability to transfer heat from the burner into your home’s pipes. Over time, this can cause your AO Smith water heater not to heat water hot enough (if at all).

wear and tear

Rust becomes prevalent when iron reacts with oxygen in water over time. This reaction causes corrosion on the metal parts inside your water tank, eventually leading to those parts breaking down entirely or becoming stuck together during operation. 

The invasion of rust in your AO Smith water heater does not allow the proper functionality needed during heating cycles, thus causing lower temperatures. 

Sometimes attempting to run the system normally would require replacing the entire unit instead of just replacing worn-out pieces individually.


You can sometimes identify the problem with your AO Smith water tank through a visual inspection. However, if the tank is rusty or has a sediment build-up, you should flush it. If your thermocouple is burnt out, you will need to replace it. 

One of these quick fixes may solve your water heater problem. If not, contact AO Smith’s warranty service, or schedule a repair. 

Hopefully, you won’t have to replace your water heater, but if you do, consider a newer model because they are more efficient and can help lower your bills in the long run.