Pilot light keeps going out on water heater

I'm at my wit's end with this. About 5 days ago, the pilot light on my water heater blew out. I reli t it. Lasted one day. Blew out again. Pulled out the burner assembly, replaced the thermocouple. Relit it. Lasted 15 hours. Blew out again. Took out the burner assembly, cleaned everything in sight .. pilot lasted around 8 hours. There are no new entrways for drafts so I don't think its a draft issue...but to be on the safe side I stuffed every potential air leaking crack.
I tend no to think it's a chimney issue as I've got a boiler also on that chimney and I have no problem with the boiler. The draft on the chimney is excellent. I'm down to two theories....one is the gas valve. Is this a realistic issue? I've checked to see what happens when I go from full on to pilot and back to full on and back to pilot and back to full on. It goes back and forth on each setting with no problem. The second explanatiion might be the "popping" effect that sometimes comes with gas abruptly shutting off....perhaps it's possible that the gas is now "popping" when it turns back to pilot and the force of the "pop" blows out the pilot. Any and all suggestions gratefully received!
Thanks........Art
email to snipped-for-privacy@croton10520.com (Leave out NOSPAM when replying)
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My thought is that it would take a pretty strong 'gust' to blow out the pilotlight, particularly if it's just suddenly started happening and you haven't been having unusually strong winds.
My bet is it's the valve. The thermocouple itself could cause this, but generally they are either good or they aren't, and since you've eliminated that as a possibility (good choice since they are cheap and easily replaced) I'd vote that you need to replace the valve.
You don't say how old the tank is, and I don't know the price a a valve, but if the tank is getting old, you might want to compare the price of a new tank to the price of the valve.
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I think you're right. I'm replacing the water heater today. The valve costs $77, the water heater costs $202. Math wins! Thanks a lot for your response!
Art...............
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Your water heater doesn't have a power vent on top does it? (That is, a blower motor). I once replaced a number of thermocouples, only to find out that one of the sensors (that determines if the exhaust gases are being drawn off the top) was bad. Two sensors kept shutting off the gas. Manufacturer's rep came out and snipped the wires to one of them saying two sensors were overkill. Solved the problem. Don't use this solution, but consider the cause if you have a power vent top.
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Art:
The boiler starting may cause the water heater pilot to "snuff". To check this make sure the water heater is just burning the pilot and have another person turn up the thermostat...if the water heater pilot "snuffs"...it is time to contact your favorite HVAC pro to check gas pressures.
"snuff"= Lancaster county PA for getting real small or going away
Vic Plank Lancaster PA
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A good suggestion....I tried it but no....that's not it. Thanks so much for your response!
Art
"snuff" = New York City for killing someone unfortunate enough to talk to me before morning coffee

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Maybe the tank has a crack in it. When the burner comes on to heat the water, the tank expands and drip water on the pilot. It happen to me had to replace the tank it was only about 7yrs old.

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Actually, a good suggestion. My friend the plumber suggested it too so you're in good company. But alas, that doesn't seem to be it. But thanks for your help!!
Art
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