# A.o. Smith promax water heater won't stay lit



## Yodaman (Mar 9, 2015)

Should be a flame sensor in there that detects the burner on. It sends a low voltage signal back to the gas valve. They need cleaning occasionally. Also, if your tank is still under warranty, there should be a toll free # for support on the side of the tank. I have called them in the past with good results.


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## cinno (Jul 14, 2017)

Had a similar problem on my 5 year old 50 gal AO Smith water heater. It has the electronic start with the traditional thermocouple for flame detector. It would try to light three times then lock itself off. My son had this problem on his AO Smith unit as well. He simply cleaned the thermocouple with steel wool every 6 months as opposed to replacing it. I looked into the problem a little further and after extensive internet searching, I found the someone that had the solution to my problem. The reason it was flaming out was because the flame is not receiving enough air and not getting hot enough to heat the thermocouple within the few seconds after lighting. The low flame temp also create deposits on the thermocouple which further reduces the response time of the thermocouple, hence the requirement to clean it often. Now the fix: These AO Smith water heaters have a FLAME ARRESTER under the flame assemble, it looks and acts like a filter but it is not, however it gets clogged like a filter and restricts air flow to the main flame. You might notice how when opening the access plate to the flame assembly, doing so dramatically effects the color of the flame. This occurs because the air now comes threw this opening and blows across the flame instead of coming threw the clogged flame arrestor BELOW the flame assembly. The solution is to clean the flame arrestor. Unfortunately it is in a tight spot so search for "TightSpot Vacuum Brush" on the internet. No where in the maintenance manual does it mention this flame arrestor or the necessity to clean it. The tight spot brush costs about $20 bucks. After cleaning everything worked great on mine, no more flame outs. 

Good luck


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## Nealtw (Jun 22, 2017)

cinno said:


> Had a similar problem on my 5 year old 50 gal AO Smith water heater. It has the electronic start with the traditional thermocouple for flame detector. It would try to light three times then lock itself off. My son had this problem on his AO Smith unit as well. He simply cleaned the thermocouple with steel wool every 6 months as opposed to replacing it. I looked into the problem a little further and after extensive internet searching, I found the someone that had the solution to my problem. The reason it was flaming out was because the flame is not receiving enough air and not getting hot enough to heat the thermocouple within the few seconds after lighting. The low flame temp also create deposits on the thermocouple which further reduces the response time of the thermocouple, hence the requirement to clean it often. Now the fix: These AO Smith water heaters have a FLAME ARRESTER under the flame assemble, it looks and acts like a filter but it is not, however it gets clogged like a filter and restricts air flow to the main flame. You might notice how when opening the access plate to the flame assembly, doing so dramatically effects the color of the flame. This occurs because the air now comes threw this opening and blows across the flame instead of coming threw the clogged flame arrestor BELOW the flame assembly. The solution is to clean the flame arrestor. Unfortunately it is in a tight spot so search for "TightSpot Vacuum Brush" on the internet. No where in the maintenance manual does it mention this flame arrestor or the necessity to clean it. The tight spot brush costs about $20 bucks. After cleaning everything worked great on mine, no more flame outs.
> 
> Good luck


That is great info.:vs_bulb:


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## Gorilla03 (Jun 15, 2016)

So here's a little update, i was told by the plumbing and heating repair man that he replaces a ton of these thermocouples, it was in such bad shape that he said that they can be cleaned but it would just happen again in the not so distant future. So I decided to get the part replaced costed me $240 installed. Fast forward to yesterday, I happen to hear the water heater cycle 3 time before shutting down and giving me a ignition /flame failure code. The only difference between the previous problem and now is that it doesn't ignite at all. Any thoughts? Does this sound like the part that was installed failed? I do want to note that yesterday before I left for the day I unplugged and shut the gas off to the unit, and when I came home turned everything back on and the unit worked overnight til this morning. It's almost to the point where if I need to spend another $240 into this thing, I feel I would be better off investing it into a new unit that isn't a.o. Smith.


Sent from my iPhone using Tapatalk


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## cinno (Jul 14, 2017)

cinno said:


> Had a similar problem on my 5 year old 50 gal AO Smith water heater. It has the electronic start with the traditional thermocouple for flame detector. It would try to light three times then lock itself off. My son had this problem on his AO Smith unit as well. He simply cleaned the thermocouple with steel wool every 6 months as opposed to replacing it. I looked into the problem a little further and after extensive internet searching, I found the someone that had the solution to my problem. The reason it was flaming out was because the flame is not receiving enough air and not getting hot enough to heat the thermocouple within the few seconds after lighting. The low flame temp also create deposits on the thermocouple which further reduces the response time of the thermocouple, hence the requirement to clean it often. Now the fix: These AO Smith water heaters have a FLAME ARRESTER under the flame assemble, it looks and acts like a filter but it is not, however it gets clogged like a filter and restricts air flow to the main flame. You might notice how when opening the access plate to the flame assembly, doing so dramatically effects the color of the flame. This occurs because the air now comes threw this opening and blows across the flame instead of coming threw the clogged flame arrestor BELOW the flame assembly. The solution is to clean the flame arrestor. Unfortunately it is in a tight spot so search for "TightSpot Vacuum Brush" on the internet. No where in the maintenance manual does it mention this flame arrestor or the necessity to clean it. The tight spot brush costs about $20 bucks. After cleaning everything worked great on mine, no more flame outs.
> 
> Good luck


Further info dated 03/23/2021: Continued to have intermittent flame detector problems, since my last post. Interesting that my Lennox furnace was having problems as well. Flame out issues became more frequent on both so I decided they must have some common issue. That issue was gas pressure regulation problems. Both the furnace and water heater were replaced at the same time when my home was upgraded to natural gas from fuel oil in 2012. A common gas regulator was chosen by the installer. I purchased a precision gas pressure gage and found the outlet pressure on that regulator was going below the minimum pressure required to operate the furnace and water heater when both units fired at the same time, this pressure drop caused a drop in flame temp which triggered a flame out alarm. Installed a new regulator rated at the combined flow rate of each appliance and set the regulated output of the regulator above the minimum pressure when both were operating together. Problem solved I believe, time will tell.


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## dj3 (Apr 27, 2020)

Have you tried calling customer service?
Have your model and serial numbers ready.
It could still be under warranty. 
Let us know what they said.


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## dj3 (Apr 27, 2020)

cinno said:


> Further info dated 03/23/2021: Continued to have intermittent flame detector problems, since my last post. Interesting that my Lennox furnace was having problems as well. Flame out issues became more frequent on both so I decided they must have some common issue. That issue was gas pressure regulation problems. Both the furnace and water heater were replaced at the same time when my home was upgraded to natural gas from fuel oil in 2012. A common gas regulator was chosen by the installer. I purchased a precision gas pressure gage and found the outlet pressure on that regulator was going below the minimum pressure required to operate the furnace and water heater when both units fired at the same time, this pressure drop caused a drop in flame temp which triggered a flame out alarm. Installed a new regulator rated at the combined flow rate of each appliance and set the regulated output of the regulator above the minimum pressure when both were operating together. Problem solved I believe, time will tell.


How much did you pay for the gas regulator, and how much for labor ?


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