pilot light won't stay lit

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Old 04-10-04, 04:12 PM
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pilot light won't stay lit

Have an old furnace. Over 40 years old. All of a sudden, the pilot light cuts out. Can get it lit, but won't stay lit.

1) any hints on what i should replace? should i just replace the whole pilot assy?

2) there are two metal pipes running to pilot.

one narrow copper pipe going directly to it and one aluminum pipe right next to it. i'm pretty sure the copper one is gas, but i'm not sure. does anyone know?

thanks
fdonger
 
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Old 04-10-04, 04:30 PM
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one narrow copper pipe going directly to it
Sounds like its the thermocouple T/C. Turn power off and gas off.Take it out and get one just like it. clean the pilot there out with can air to blowon it if you can. Put the new T/C back in as was. Hand start the the end into the gas valve so you dont cross thread it

one aluminum pipe right next to it.
This should be the gas line .

turn power on gas on and light the pilot again should hold for you.

ED
 
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Old 04-11-04, 11:13 AM
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ok...

i replaced the thermocouple/pilot assy. turned gas and power back on. tried to light the pilot.

i had the pilot knowb depresssed for a few minutes and the pilot wouldn't stay lit.

1) do i need to light it and hold it for a long time initially?
2) i would think lighting the pilot would be independent of anything else in the system. is that true?

am i missing something?

donger
 
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Old 04-11-04, 11:26 AM
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maybe i don't understand how a pilot light stays lit.

i didn't think this was the case, but does a consistent input of gas keep the pilot light lit? if so, then there is a feedback mechanism through the thermocouple that keeps the gas on when i let the pilot knob release.

if i've replaced the pilot thermocouple assy and it won't stay lit, it must be the control unit that's bad.

am i on the right track?

donger
 
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Old 04-11-04, 12:51 PM
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Hello: donger

Before assuming the control is defective, try another thermocouple. New ones can be defective.

Also try cleaning the end of the T-Couple and the inside upper end inside the control. Use nothing but a cotton swab. No chemicals, etc.

Be sure the element end of the T-Couple in the pilot assembly is correctly in place. Only the tip of the T-Couple is to be heated. About a 1/4 inch of the tip.

The heat the pilot flame provides to the T-Couple allows the T-Couple to generate a small amount of dc volts. About 1/4 volt. Which is used by the magneto inside the control to hold the tiny pilot gas valve opened.
 
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Old 04-12-04, 09:08 AM
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thanks sharp advice.

i'm glad u bring it up. the tip isn't positioned very well in relation to the gas valve. the flame is definitley not hitting the top 1/4" of the tip. i tried repositioning, but to no avail. looks like i will need to get a new fixture for the gas valve/thermocouple. i didn't see these at the home depot.

i guess i'll try some specialty shop.

i did get a longer thermocouple as well. you think this will make a difference? i figure as long as the connection is there, it would be okay.

donger
 
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Old 04-12-04, 09:18 AM
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the flame is definitley not hitting the top 1/4" of the tip. i tried repositioning, but to no avail.
Most of the thermocouples come with a kit that has a lot of adapters to fit most types of pilot burners. You sure that you have the right one in there so the T/C will go in the flame ??



ED
 
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Old 04-13-04, 12:50 PM
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if the pilot orifice is dirty, it will make a BIG diffefence on how well the flame hits the thermocouple. i would clean it and try again. at 40 yrs old, those parts are brittle, be very careful, or just replace the pilot assy, which is what i would do.
 
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