Solve the gas water heater mystery

I have a Rheem 50 gal gas water heater (21V50-2) and need a little help in isolating the problem. Based on some of the post I read on this NG it will likely be "layup" for someone.
So a few days ago the pilot lit went out, and now to days later it won't stay lit. Here are the tests I have done, any suggestions on which component is failing?
1. The pilot flame looks normal so I don't think there is an issue with this.
2. I can turn thermostat all the way down to "vacation" and the pilot will stay lit by it self all night.
3. There seems to be a lot of heat coming out of the lower panel that pilot light feeds through. The outside sidewall of the heater right about this panel opening is starting to mis-color from the heater (brownish). I have had the panel cover off a bit lately but there does still seem to be an unusual amount of heat coming out.
4. Once lighted and on med-hi to high I only get about 20mins before burner and pilot goes out. I am not sure if it's relevant but when all the hot water is out and the heater has to heat all 50 gallons from cold to hot I still can only get 20 mins out of it. If I turn the temp down to low it will stay lit a lot longer.
Please let me know if you have any suggestions on what the problem is.
Thanks, Paul
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Paul in Boise wrote:

Sounds like possibly a regulator/pressure problem if both are going out under load and not when in vacation--sounds like it isn't getting enough gas--sorta like starving an engine.
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Wow, guess it isn't as simple as I thought. I appreciate the responses. I guess I would like to ask another question though. Are there any simple tests that I can do to further isolate the problem? I don't have any specialized tools but if there are any tricks you may know that might elimate a few things please just let me know. Also, it looks pretty easy to remove the pilot light for cleaner but how do clean it once it's out. Thanks again!
BTW, this heater was new with the house in 1994.
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Try all the suggestions received.
With a 10 year old heater the control valve could be bad. They aren't worth replacing. They cost almost as much as a new heater IF you can even remove the old one from the heater.
If you take apart the pilot to clean it replace the thermocouple at the same. Now you are gambling $6 and 2-3 hours against the cost of a new heater.
Remove the pilot assembly. Remove all the ash and crud from the pilot burner with a stiff tooth brush (wire preferred). Take it apart. Give the pipe a good BG. Inside of the burner there is an orifice. The look varies but what it is a very tiny hole through which the gas passes. When held up to a strong light you should see a perfect circle. Most likely you won't. Your job is to clean the hole so that when sighted against a strong light you see a perfect circle. You MUST NOT enlarge the hole by using a needle or item to big to clean it. I have had good luck using a single strand of wire from a twisted galvanized wire (such as antenna guy wire). You need to use something about half the size of the point on the safety pins that the dry cleaners send back on your clothes. When you see the perfect circle the lint or dust has been removed. The pilot should burn higher and wider than it did before you cleaned it.
Test all connections that you loosened with a solution of 1 tablespoon of dish soap to 16 ounces of water. If any connection blows bubbles tighten till it does not. Don't confuse the tiny bubbles from the soapy water as being a leak. They will grow if you have a leak.
As always you accept this mission at your own risk. The information provided is believed accurate but your are responsible for the final determination as to the accuracy and or the results.
Colbyt
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Thanks!
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Most likely this will not solve the problem but it is worth a try.
Gently tighten the connection where the thermocouple is connected to the gas valve. No more 1/4 turn at very moderate pressure.
Replacing the thermocouple if it looks burnt or the unit is older is another option though usually they don't stay lit at all if they are bad.
Colbyt
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Start with the thermocuple, while at it flush the tank of scale, it wont help your problems but will increase efficiency
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On 13 Feb 2005 10:58:05 -0800, "Paul in Boise"

Clean the pilot head. Replace the thermocouple. Temp setting has nothing to do with the pilot going out. Check the venting and proper chimney sizing to keep the flue gases going up and out the chimney and not down drafting back out the front of the water heater. If its and old water heater ( 10 yrs or so) think about replacing it. Bubba
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With the heat coming out the bottom, makes me wonder if you've got a clogged chimney?
Might be choking the flame for lack of oxygen?
--

Christopher A. Young
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clogged
Good point Chris.
To test for a blocked flue hold a burning match under the draft hood while the main burner is burning. If the flame draws toward the chimney all is fine. If the match blows out, you have a draft/venting problem.
Colbyt
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Colbyt wrote:

More in that vein: A number of times we have seen the inner flue passage *inside* the heater collapse. The pressure of the water crushes a tank core weakened by age and rust.
The flame burns out because of lack of oxygen. Usually gives off a very bad odor when it does. This type of failure may not show on the draft hood test.
Jim
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Exactly, I had a Rheem heater that failed in this manner. The flue stack had collapsed. One sign of the impending collapse was large piles of rust flakes in the burner chamber.
A possible accelerator of this process was my use of chlorinated degreasing solvents (gun cleaner) in the basement. This stuff breaks down in the flame, releasing chlorine, which combines with combusion moisture, which condenses as acid on the inside of the stack.
One way to prove this. Move the draft hoof and flue pipe aside, and try to lift the baffle plate out of the heater stack. If it won't move, then the stack has collapsed.
To reply, please remove one letter from each side of "@" Spammers are VERMIN. Please kill them all.
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Liberal gun haters design water heater tanks, now?
--

Christopher A. Young
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