AO Smith Gas Water Heater Troubleshooting

9 AO Smith Gas Water Heater Troubleshooting Tips

This is a complete guide on AO Smith Gas Water Heater Troubleshooting. What common problems I am going to break down are: 

  • Take too long to get hot water at water fixtures
  • Not enough hot water
  • Too hot water
  • Hot water is not available when a fix is opened
  • Hot water turns cold and stay cold
  • Pilot light won’t light
  • Pilot light keeps going out repeatedly
  • Pilot light won’t stay lit
  • Unit makes unusual noise

So, let’s get started right here. 

Table of Contents

AO Smith Gas Water Heater Troubleshooting [9 Common Problems & Solutions]

This chapter will disclose everything you need to know when your AO Smith Gas Water Heater doesn’t function properly.

01. Take A Long Time To Get Hot Water

How much time it will take to get hot water from the water heater to your fixtures depends on the length of the pipe between the two. If the length of the pipe is longer, it will take time to take hot water coming out of the unit at your fixtures. The water needs to travel a long way. 

How To Fix: 

Apparently, it’s not a problem at all. If you wish to receive hot water at your fixtures quickly, you can install a hot water circulation system. Regarding this, you should hire a professional plumber. 

02. Not Enough Hot Water

Your AO Smith Gas Water Heater won’t provide sufficient hot water due to the following reasons:

  • Plumbing connections between cold water lines and hot water lines get reversed. 
  • Gas supply valve is not fully open
  • Size the gas pipe improperly
  • Insufficient gas supply pressure 
  • You may set the temperature too low

How To Fix: 

First off, check the plumbing connections. Ensure you don’t make a mistake connecting the cold water lines and hot water lines. 

Secondly, you should keep the gas supply valve fully opened. If you partially open the valve, your water heater will not get the amount of gas it needs to ignite the heater. So, take a look at the gas supply valve and fully open it. 

Thirdly, make sure you size the gas pipe properly for the unit using ANSI Z223.1/NFPA 54 in the USA or B149.1 in Canada. Without sizing the gas line correctly, your water heater doesn’t receive the right volume of gas for smooth operation. 

Take a look at the following screenshot and size up the gas pipe if you operate the water heater with natural gas: 

Natural gas supply piping

On the other hand, you should size up the piping according to the below screenshot for a water heater operated by propane gas: 

Propane Supply Piping

Next, what you need to do is- measure the inlet gas supply pressure. If you get insufficient gas pressure, the water heater fails to heat the water properly. The ideal inlet gas pressure is: 

Gas Type Inlet Gas Pressure
NaturalMin. 4.0” W.C. (1.00 kPa) – Max. 10.5” W.C. (2.61 kPa)
PropaneMin. 8.0” W.C. (1.99 kPa) – Max. 14.0” W.C. (3.48 kPa)

To measure the inlet gas pressure, follow the below steps: 

  • Turn the gas supply off by shutting the manual gas valve on the gas supply line.
  • Pull out the screw from the pressure port located on the gas inlet of the unit. 
  • Attach the manometer to the pressure port and set it to zero. 
  • Open the manual gas valve again. 
  • Turn off all the gas burning equipment and take a reading of the static gas pressure. 
  • Now, measure the gas supply pressure at maximum heater operation. To operate the heater at maximum, open hot water faucets and press the MAX button on the computer board. 
  • Measure the supply dynamic gas pressure with all gas burning equipment on at maximum rate. 
  • The static and the dynamic gas pressure should be within the ranges mentioned in the above table. The differences shouldn’t exceed 1.5” WC. If the pressure drops that exceed 1.5” WC, understand the gas flow gets restricted or you size up the gas lines wrongly. 

I highly recommend you call a certified plumber if there is a gas pressure issue. 

Lastly, adjust the temperature setting using the DIP switch if you set it too low. 

03. Too Hot Water

If you set the temperature setting too high, you will get excessive hot water out of your AO Smith Gas water heater. 

How To Fix: 

It’s pretty simple to reduce the temperature of the unit. Just locate the DIP switch and set it to your desired temperature setting. On the other hand, you can also use the remote control to set the temperature with ease. 

04. Hot Water Is Not Available When A Fixture Is Opened

Don’t you get hot water when the fixture is at an open position? Then, one of the following reasons is responsible for this problem: 

  • You may partially open the gas supply valve
  • Partially open the water supply valve
  • Filter on the cold water inlet gets clogged
  • You may not open the hot water fixtures sufficiently to draw at least 0.5 GPM through the water heater.
  • The unit gets frozen
  • Insufficient gas in the tank

How To Fix: 

First off, check the gas supply valve. Make sure you turn it fully to a clockwise position to let gas flow freely.  

Then, take your eyes to the water supply valve. You should also fully open the valve for continuous water flow.  

3rdly, you should inspect the filter on the cold water inlet. If it gets clogged, you will get no hot water at your fixtures. You must drain the water to access the filter. So, check your water heater manual and drain it. 

Once you drain the tank, locate the water filter which you can find within the cold inlet. 

Pull out the water filter and use a tiny brush to suck away dirt and debris accumulation. After cleaning it, replace it into the cold water inlet. 

Fourthly, ensure you fully open the hot water fixtures. Typically, you need at least 0.5 GPM at the default set temperature to activate the water heater. If you don’t open the hot fixtures sufficiently, you will not receive enough hot water from the unit. 

Fifthly, ensure the piping within the water heater doesn’t get frozen up. AO Smith Water Heater comes with a freeze protection system. Once this sensor senses air temperature below 36.5-degree F, the heating blocks will heat up to prevent freezing up the water heater. 

Note: The pipes that come within the water heater are only protected by the freeze protection system. Other pipes located outside the unit won’t be protected. So, what you need to do is- insulate those pipes. 

Finally, check the propane tank to ensure there is sufficient gas. If not, bring it to your local gas station to fill it up. 

05. Hot Water Turns Cold And Stays Cold

If you experience this problem, my first suspicion is- the flow rate is not enough to keep the water heater running. Second, the recirculation line doesn’t have enough check valves if you installed a recirculation system. Thirdly, the water fixtures may get clogged. 

How To Fix: 

At default temperature setting, the flow rate should be 0.5 GPM to activate the water heater. To keep the water heater running, the flow rate should be 0.4 GPM. 

Next, ensure the recirculation line has enough check valves and you open them fully so that they provide no less than 2 GPM and no more than 4 GPM through each activated unit in the system. 

Nonetheless, don’t forget to check the water fixtures for a clog. Release the blockage to get continuous water flow. 

06. Pilot Light Won’t Light

This problem basically occurs for new installations. Your AO Smith Gas Water Heater pilot light won’t light if: 

  • You don’t turn the manual gas shut-off valve to the on position.
  • Air in the pilot tube and the gas supply line.
  • Igniter produces no spark. 

How To Fix: 

I suggest you begin with checking the position of the manual gas shut-off valve. You can find it in the supply line to your water heater. Ensure you set it to the on position. Otherwise, no gas will flow to the burner chamber for combustion.  

Secondly, you must purge the air from the pilot tube and gas supply line. To do that, hold the gas control knob inward for 5 minutes to let all the air bleed. You can also run hot water faucets to purge the air. Once you get a continuous water flow, turn off the faucets. 

And thirdly, take a look through the transparent glass window to see whether the igniter produces a spark or not. If not, you should test the igniter system. Go along with these steps to test the igniter: 

  • Turn the gas supply off at the manual gas shut-off valve.
  • Take your eyes on the electrode tip while activating the igniter. You can see a spark from the electrode. 
  • Don’t touch the burner or other metal parts in the pilot or the pilot assembly. 
  • If you see no sparks, check the wire connections.
  • You must replace the defective igniter if the wiring is ok. 

And this video will help you replace the spark igniter on your AO Smith Gas Water Heater: 

Dirt and rust on the electrode tip can also prevent the igniter from producing no sparks. Use an emery cloth to clean the electrode tip. 

07. Pilot Light Keeps Going Out

The pilot light of your AO Smith Gas Water Heater will keep going out repeatedly because of: 

  • A dirty base-ring filter
  • A clogged flame arrestor 
  • The flame arrestor show signs of discoloration

How To Fix: 

If you use the AO Smith Gas Water Heater for years, it’s possible the base-ring filter gets dirty due to lint and debris. You should inspect and clean the base-ring filter at least once a year. Now, let’s see how to clean the base-ring filter: 

  • Turn off your water heater and leave it for 10 minutes to let the unit cool down.
  • Get a vacuum cleaner with a hose attachment and use it to suck away dirt and debris from the base-ring. 
  • Once you clean the base ring, you should relight the pilot. If you don’t know how to light the pilot, keep reading as I will break it down at the end of this guide. 

Secondly, you should inspect the combustion chamber and the flame arrestor for a clog. If dirt and debris make their home there, it will smother the flame as air can’t enter the combustion chamber. 

To clean the combustion chamber and the flame arrestor, you must remove the burner assembly from the unit. So, turn the gas supply off to the unit. Then, remove all the lines attached to the gas control valve. 

Next, unscrew the burner assembly door. Then, remove the burner assembly. Now, use a vacuum cleaner with hose attachment to clean the arrestor and the combustion chamber. 

And finally, replace everything back into their places. 

If you notice any sign of discoloration on the flame arrestor, turn the gas supply off and call a certified plumber to deal with this issue. 

08. Pilot Light Won’t Stay Lit

Your AO Smith Gas Water Heater pilot light won’t stay lit due to insufficient combustion air. Your water heater pilot light will also struggle to remain lit if the return air duct for the furnace or the air conditioner draws its air from the same location as the water heater. Besides, improper drafting and clogged vent systems are responsible for the pilot light to not stay lit. 

How To Fix: 

If your water heater gets insufficient air for combustion, the pilot will never stay lit. So, what you need to do is- ensure you have the correct size of air supply and ventilation openings. I highly recommend you call a certified plumber to fix this issue for you.  

Secondly, contact a heating & air conditioner technician to relocate the return air duct. It will extinguish your water heater pilot light when you turn on the heating or the cooling system if the return air duct is in the same location. 

Improper drafting can also prevent the pilot light from staying lit. You should run a draft test to see whether the drafting is ok or not. For this, light the pilot and run the water heater for 15 minutes. Then, inspect the draft hood relief openings for proper draft. 

Now, light up a match and ensure the flame is drawing into the relief opening. If the flame is not drawing, there is an issue with the drafting. In this case, turn off the unit and don’t run the water heater until you make a proper adjustment. 

Lastly, inspect the vent system for blockage and release the blockage if needed. If still the pilot light is not staying lit, call a certified plumber to handle this pilot issue.  

09. Unit Makes Abnormal Sound

Does your AO Smith Water Heater produce abnormal noise when operating? If yes, you need to turn the unit off right off the bat and call a professional. 

How To Fix: 

It’s not a problem you can solve yourself. So, it is better to leave this task for professionals to stop the unusual noise. 

How To Light Pilot Light On AO Smith Gas Water Heater?

Before lighting the pilot light, you should maintain the safety tips. For example, you should never open the inner door of this unit and try to light the pilot by hand. 

If you smell gas, don’t dare to operate the unit and call the gas supplier company for help. Don’t use your own phone; make a call using your neighbor’s phone. Never use any tool to push or turn the gas control knob. 

Once you meet these safety tips, follow the below steps to light the pilot. 

  • Set the gas control knob to the off position by turning it counter-clockwise. 
  • Wait for 10 minutes to let all the gas clear out. 
  • Turn the gas control knob to the Pilot position by turning it clockwise. 
  • Hold down the gas control knob all the way in. While holding down the gas control knob, start depressing the igniter button continuously like up to 90 seconds or until the status light starts blinking. 
  • Release the gas control knob when the status light starts blinking and set the gas control knob to the desired temperature settings. 

Note: If the pilot light doesn’t come on after the first attempt, try another two to three attempts to light the pilot. Otherwise, you should turn the gas control knob to the off position and call a professional for help. 


Over time, every appliance starts malfunctioning. Your AO Smith Gas Water Heater is not an exception to that. Improper operation doesn’t mean you should call a professional and spend money. If you know how to troubleshoot the water heater, it will save you both time and money. And AO Smith Gas Water Heater Troubleshooting Guide is what comes into play when your heater doesn’t function as intended. So, bookmark it so that you can use it when needed.  

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  1. I replaced the pressure relief because it was dripping now the new one drips after the tank reheats . Tank is 6 years old

  2. One month into using 75 gal ppg model stopped working 3 times.
    Relit each time and it turned on.
    This is a second unit I installed within last year with same problem.
    What is causing it?

    1. Hello Henry,

      Give more in-depth about your problem. However, it would be best to contact a certified service personnel if you unable to turn on the unit by relighting it.


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