Hot water heater pilot won't stay lit


  #1  
Old 10-16-05, 12:58 PM
Ray_M
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Hot water heater pilot won't stay lit

I have an AO Smith water heater (model FSG 50 248), about 3 years old. It worked fine until I shut it down (gas & water) so we could evacuate for Hurricane Rita. When we came back, (no Rita damage), the pilot light would not stay lit.

The pilot flame burns just like it should, as long as the gas valve knob is kept pushed down, but it goes out as soon as the knob is released.

A plumber looked at it and quoted us $350 to fix it, or $1200 for a whole new water heater (it's in the attic of a 3-story town house). OUCH!

So here I am trying the do-it-yourself route. "For other reasons" (I bunged up the pilot gas tube), I replaced the entire burner unit (burner, pilot gas tube, thermostat). Same problem.
So I checked the thermocouple by heating the tip on my stove. It read about 27 mV. Tested the old one too and it read the same thing. Then I reinstalled everything - except before connecting the thermocouple to the gas control valve, I checked that it gave a similar voltage. So I reconnected and tried one more time. Same problem.

SO MY QUESTIONS: Is it the gas control valve that's faulty? If so, how could the shut-in have caused it to fail? And should I replace it or just gut up and get a whole new water heater?

Any help appreciated! ( After 2 weeks, cold showers are getting old!)
 
  #2  
Old 10-16-05, 05:07 PM
H
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Only three things will cause the symptoms you're describing. If you checked the thermocouple, that would leave only two.

1) The spill switch (if installed) is tripping.

2) Faulty gas valve.

If there is no spill switch on the heater (it's not required in many places), it is a bad valve. For a three year old heater, you likely better off replacing the gas valve only. You likely have a few years left on your tank warranty.

How could a shutting down the heater cause it to go bad? It happens. The magnet could have been getting weak prior to the shut down, but was strong enough to keep the gas flowing. Once it was shut down, the magnet wasn't strong enough to start the heater back up.
 
  #3  
Old 10-17-05, 05:02 PM
Ray_M
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Thanks! Time to buy a gas valve.

Thanks! Time to buy a gas valve.
 

Last edited by mattison; 10-21-05 at 04:55 AM. Reason: No need to quote the entire post above. Thanks.
  #4  
Old 10-17-05, 05:20 PM
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Since you are going to replace the gas valve anyway, which is most likely your problem, Try tightening the thermocouple in 1/4 turn steps and then try to relight at each turn. No harm in trying. I have had this work many times over the years. Don't worry about over tightening since you will be replacing the valve if this doesn't work.
 
  #5  
Old 10-19-05, 06:58 PM
Ray_M
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Thanks for the tip. I tried it, even used some fine emery paper to clean off the end of the thermocouple, then scrunched it down tight - until the flats on the brass bushing started to give way. Still no success, but it was definitely worth the try.
 

Last edited by mattison; 10-21-05 at 04:55 AM.
  #6  
Old 10-19-05, 09:20 PM
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[QUOTE=Ray_M]

So here I am trying the do-it-yourself route. "For other reasons" (I bunged up the pilot gas tube), I replaced the entire burner unit (burner, pilot gas tube, thermostat). Same problem.

Somthing isn't ringing right here. You have replaced everything except the tank. You must have left something out. At this point all I can think of is the t'couple is not on the pilot flame.
BTW the way you tested t'couple is called an open read and means little. The proper way is to do a closed read, meaning t'couple is installed in systemwhen tested. Open could show 27mv and closed 0-1-2 which is considered dead.
 
  #7  
Old 10-20-05, 04:58 PM
Ray_M
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OOPs! I wrote 'thermostat' but was thinking 'thermocouple'. I have not replaced thermostat yet. The thermocouple is definitely directly in the pilot flame. Hadn't heard of the proper way to test thermocouple - thanks. I don't know how to set it up to measure in the system itself. Like testing a car battery under load I suppose. So what is correct test procedure, and what is correct result - number of milliamps it can deliver, millivolts under load? (and if I read your note right, 0-1-2 mV under load would be 'dead', and would indicate a new thermocouple is needed?). I did replace the old thermo'couple' with a new one, no change in result. Called AOSmith and they said it sounded like the thermo'stat' ('gas control valve' to me).
 

Last edited by mattison; 10-21-05 at 04:56 AM.
  #8  
Old 10-20-05, 07:46 PM
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Testing t'couple under load requires an adapter, which I wouldn't worry about in your case since you already replace t'couple. Yep sounds like time for new control.
 
  #9  
Old 10-23-05, 05:05 AM
Ray_M
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Warning! DON'T light your pilot light with a propane torch.

The note string above all began after Hurricane Rita, after my gas hot water heater pilot wouldn't stay lit. (I mentioned 'I bunged up the pilot' well this is how).
We got back from the evacuation after a long long drive, found no damage. I was very tired but we needed to turn the hot water back on. The hot water heater is not in a convenient location - up in the attic. I couldnt get the cover plates off to access the pilot (or was too tired to bother) but there was a small hole where the burner tube, thermocouple and pilot tube go in. So I turned on my propane torch and stuck it in since it could reach in near the pilot itself.
Later, since the pilot wouldn't stay lit, I did pull the cover plates off and looked in to see the pilot flame, plus a second flame coming out the side of the pilot gas line -- a hole!
Much later, after replacing the pilot gas line, I took the burner to the old gas line and tried it out. In 10 seconds, the line melted in two and fell apart!
Seems odd that a low-melting point material would be used in a burner assembly, but then the flame ian't usually supposed to go down either.
In hindsight, I'm wondering "well DUH, how could you be so stupid" but it all seamed logical at the time.
 
  #10  
Old 11-10-05, 09:26 AM
Ray_M
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Thermostat fixed it!

Just to close the loop, I finally got the replacement thermostat (gas control valve) and replaced it. The pilot lit, then the burner lit first try, and stayed on! Thanks for the advice.
 
  #11  
Old 07-20-07, 03:23 AM
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Unhappy Help!

I am female live alone and having the same problem...got up for work at 430am to take a shower...BRRRRR! I have the same water heater but with an electrical sstarter switch. Same problem...pilot won't stay lit. I don't know if I should disassemble it to clean it or have a pro do it. I'm pretty good with understanding stuff like this. What do you think. I know your post is pretty old but in hope that maybe you'll see this.

Need to shower in Chicago!!!!
 
  #12  
Old 03-21-08, 02:40 PM
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Won't Stay Lit Either


Whenever it is windy outside, the pilot light on my hot water heater goes out and I cannot get it relit. I live in a townhouse and when I am on the floor trying to relight it, I can feel the wind blowing underneath it. Any suggestions?? I have twice paid somebody to come out and relight it and I am tired of doing that.

HELP!!!
 
  #13  
Old 03-23-08, 06:01 PM
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Defective thermocouple....think again.

My boiler was having trouble keeping the pilot light on and the more I read about it the more I thought I had a defective thermocouple. Before you go out a purchase a replacement try cleaning your old one using a scouring pad or sandpaper, make sure you remove all of the carbon and it may come back to life. Just some FYI.
 
 

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