Weird AO Smith Nat Gas Pilot light issue

Reply

  #1  
Old 07-28-20, 06:42 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
Weird AO Smith Nat Gas Pilot light issue

I have two 2006 AO Smith 40-gal ProMax gas hot water heaters. I have taken very good care of them, I flush them once a year, change the anode rods as needed, keep them clean, check for backdrafting, etc.

Last week one of them had a pilot light out and wouldn't relight. I did the following:
1. removed the burner, cleaned the filter and the disc with compressed air, I cleaned it very well.
2. I changed the thermocouple and igniter and pilot light assembly because the fuse looked like it was broken when I removed it, with a part from amazon that works with AO smith and other brands. It did appear to be an exact replacement. In fact, I used the same one on the other heater and it's working perfectly. This is basically the assembly that has the pilot light tube, the thermocouple and igniter and the gaskets, it's everything under the tank except the burner itself (which was in great condition).


Put it all back together... worked for 10 minutes, then it went out. After a few cycles I kept it running for 4 days.

So then I took it apart again and blew out the gas tube into the burner, and all connections on the gas control valve, checked the vents, made sure all connections are tight and clean, and basically everything I could check. All looked fine.

The operation valve appears to be working correctly, the thermostat is working, and the knob pops up when released and I have to hold the knob down while the thermocouple warms up (which is normal) and once the thermocouple is warm I can release the knob (all normal of course).

The pilot light seems to like to go out when the tank is cold and it heats up for the first time, once it's warm it tends to not go off as frequently. It seems to cut off completely, not go out slowly although I've only seen this once.

The pilot light is strong when on. The burner flame is normal.

I am out of things to try, other than changing the gas control valve, but on a tank this old I don't think it's worth it

Any ideas? There seems to be nothing left except for the gas control valve.
 
Sponsored Links
  #2  
Old 07-28-20, 07:38 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 58,593
Received 1,045 Votes on 969 Posts
Welcome to the forums.

AO Smith uses a cordite disc under the water heater. It's part of the safety system that shuts the unit down in case of explosive vapors. That disc is like a honeycomb and gets clogged with dust and chokes the unit for air. The thread below has the plumbing pro in it. There are actually several threads dealing with this issue.

ao-smith-water-heater-pilot-randomly-going-out.

This what I made to vacuum mine and many others.
It's a 3/4" copper 90į and about 20" of 3/4" copper pipe. I cut the 90 off as that is all the room you have to get that under the WH. No need to solder the fitting.You want to point it up when using it. I tape it into my vacuum cleaner.

 
  #3  
Old 07-28-20, 08:01 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
Hi thanks.

ĎíI completely cleaned the top and bottom of it. I have a flexible 90psi air gun that I used to blow air from both the top and bottom. I used air and not a vacuum, but the idea should be the same. I only got a small puff of dirt on the first spray. I cleaned it for 5 minutes with 90psi and a nozzle that reached underneath completely. am pretty sure itís clean. I am sort of lost.

whats even more interesting is that I heated it up to the highest setting, thinking that would force the high heat situation and trip the self resetting fuse...didnít happen.. worked fine. As crazy as it sounds, it seems like it likes to fail when the water in the tank is cold and and it heats up to normal temperature. I cannot explain that at all.

The flames are normal in appearance, thereís no dancing of the flames or downward pointing flames and the color is right.

I am thinking it must be the gas control valve, which for a heater this old means i just replace the whole heater.


 

Last edited by mikoz; 07-28-20 at 10:00 PM.
  #4  
Old 07-30-20, 06:25 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
I took apart the vent and saw that there was a black piece at the top of the outlet from the heater and it was somehow misaligned... it was actually visible without removing the vent. I donít know what itís called, itís like a huge metal washer. I guess itís there to align the flow of air out of the tube. Itís like someone picked it up and dropped it back it place in the wrong position. As a result, it was definitely impeding the air flow a bit, but not sure if it was enough to cause the problem. Iíll know in a few days.

it may make sense too, as there was enough air flow to a point, amd when you heat up the tank from cold to normal itís a long burn time so maybe that explains it. Obviously I know CO could be an issue in that scenario. The heater is in the garage and Iíve got plenty of CO detectors even in the garage so it couldnít have been that bad.
 
  #5  
Old 07-30-20, 06:38 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 58,593
Received 1,045 Votes on 969 Posts
There is a spiral piece of metal with a round ring that goes from the top of the WH to the bottom. Its job is to slow down the exhaust gases to more thoroughly extract the heat from them. That may have not been in place. Part 10 in the diagram.



 
  #6  
Old 07-30-20, 06:56 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
In the picture,yes, it’s the top of 10. It wasn’t attached to anything though, it was just floating. I have no idea why it was dislodged...makes no sense.
do you think it being misaligned could have caused high temperatures to trip the thermal fuse causing the gas flow to stop?
 
  #7  
Old 07-30-20, 07:30 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 58,593
Received 1,045 Votes on 969 Posts
I'm not the plumbing pro. He's pretty good with AO Smith water heaters.
Anything that blocks the exhaust can cause an overheat issue.
 
  #8  
Old 07-31-20, 09:15 AM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
Problem came back... happens when the heater is running for a long time, I'm stumped. It's clean, no blockages, flames look good, I replaced the entire igniter/thermocouple assembly. Seems like it must be the gas control valve... time for a new heater I guess.
 
  #9  
Old 07-31-20, 03:55 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
I started looking around at heaters, it's killing me to have to do that. it's such a simple system, but it seems like the gas control valve is turning off the gas and I'm not going to spend $120++ on a new one on a tank this old.

Seems like the AO smith @ lowes uses a plastic drain valve... yikes. Have to go to the proline, or a higher level Rheem.
 
  #10  
Old 07-31-20, 04:48 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
I have one more thing to try, I will swap the entire burner and door assembly between the heaters and see if the problem stays with the tank. Maybe I got a bad thermocouple with my replacement part... unlikely though.


I did a draft test and it's sucking in the smoke.

 
  #11  
Old 08-01-20, 04:14 PM
J
Member
Join Date: Aug 2020
Posts: 1
Received 0 Votes on 0 Posts
Pilot light wonít stay lit

I had the same problem and placed a small fan in the attic next to the water heater 3 weeks ago and itís worked so far, Temps in Houston in July are way above 100 degrees in the attic and the problem seems to occur when the outdoor temps are in the mid to high 90ís. The water heater was installed in June and the temps were in the low 90ís and the pilot light stayed lit, but once July arrived the temps were in the high 90ís or in the 100ís.
 
  #12  
Old 08-02-20, 08:02 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 10,640
Received 85 Votes on 75 Posts
Have to go to the proline, or a higher level Rheem.
Do yourself a huge favor and get a Bradford-White.
 
  #13  
Old 08-02-20, 09:02 AM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
There seems to be hope, I swapped the burners and now the problem is gone, for now. The only explanation I have is that one burner runs 190c in one heater, but when moved to the other heater it does not. I still think the chamber is getting hot enough to trip the 190c cutoff, that’s the only explanation why the pilot and burner go off together as the gas control valve seems to be ok.

is this plausible?

I also realized that I should have gotten the 200c replacement thermalcoupoe/cutoff/igniter assembly instead of the 190c version as they changed this for a reason.
 
  #14  
Old 08-02-20, 11:02 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 58,593
Received 1,045 Votes on 969 Posts
I also realized that I should have gotten the 200c replacement thermalcoupoe/cutoff/igniter assembly instead of the 190c version as they changed this for a reason.
I would agree with that. I had done that to my older AO Smith Promax.
 
  #15  
Old 08-02-20, 01:21 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
I ordered one 200C version, just to have, but since the problem doesn't seem to want to come back (yet, at least), it will be tough to figure this out. But, so far, I can say that by switching burner assemblies (both were just replaced), the problem has disappeared. It's like one burner assembly runs cooler than the other and only one heater shows the issue with 1 burner assembly. I do believe it's just the thermal cut off causing the issue, not the gas control valve or ventilation/air intake.

There's likely a real valid reason why they switched from 180 or 190 to 200C.

 
  #16  
Old 08-05-20, 01:45 PM
M
Member
Thread Starter
Join Date: Jul 2020
Posts: 10
Received 0 Votes on 0 Posts
so days now of no issue after swapping the burner assemblies between the two identical GCV40 heaters (both assemblies were refurb'ed by with 190C setups and cleaned very well). The only conclusion I have is that one burner burns hotter triggering the 190C threshold only in one heater. Weird.
I will install the 200C setup only if I have to. Seems like it must just be on the edge, one burner is just a bit different than the other in one heater... may be a small airflow difference or something ?
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: