old furnace pilot goes out after a while, thermocouple already replaced

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Old 11-08-11, 11:23 PM
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old furnace pilot goes out after a while, thermocouple already replaced

just bought an old house, it has a furnace on the floor. i cannot find a name brand or model anywhere on it.

the problem i am having is keeping the furnace pilot lit. i replaced the thermocouple. i adjusted the pilot with the screw adjuster underneath the cap. adjusting the pilot screw didnt seem to make any kind of difference on the size of the flame of the pilot. i even fully turned it counterclockwise until the screw came out. honestly, i didnt notice any difference in the pilot at all while adjusting the screw.

any ideas about anything else i can do to prevent the pilot from going out? should i replace the pilot assembly piece? is there a way to clean it?

i can't find any identifying info on the furnace, but i would guess it is 25 years old. once it lights the burners, the fan kicks on a bit later and runs alright. but then after a little while, i come back to check it and the pilot is off.

thank you
 
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Old 11-08-11, 11:28 PM
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i forgot to mention. the thermocouple is adjacent to the pilot flame, is that correct? should the thermocouple be right in the middle of the pilot flame? i tried to slightly bend the thermocouple so it is as close as possible to the pilot. would it be possible that the thermocouple is not close enough to the pilot flame, and that is why the gas is shut off to the pilot? i would say the thermocouple is 1-2 mm from the edge of the pilot flame. i tried my best to get it right in the middle of the pilot flame, that is why i tried to increase the pilot flame adjusting screw. thank you.
 
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Old 11-09-11, 10:46 AM
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the thermocouple should be immersed in the flame. the adjustment you did to the gas valve controls how much gas goes to the burners, not the pilot. sometimes when the older furnaces turn themselves off, they have a slight tendency to blow out the pilot from time to time. best thing i can recommend is that you sit in front of the furnace, light the pilot, turn the system on and then cut power to the furnace after the burners light, to simulate the furnace going off on its own. turn if off(after the burners light), on, off, on and repeat till the pilot goes out. this should give you some idea as to what is causing the pilot to go out, sometimes its too much gas pressure that causes the pilot to go off. maybe you could move the pilot assembly to the right/left side or something.
 
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Old 11-09-11, 08:00 PM
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are you sure that that adjustment i made is the gas to the two burners, and not to the pilot flame? i can gladly share that the furnace pilot has stayed on for 2 days now. so i think it is best not make anymore adjustments. it is for a rental property, so if the pilot is wasting a bit more gas than needed, its not a big concern of mine. but back to the first line, everywhere i have read it said that the the adjustment screw underneath a screw cap is the adjustment for the pilot.

I noticed on the side of the control box there is an adjustment with an allen wrench, i will post what it says on it. i can't remember off the top of my head but i do remember that it is an allan wrench and there was something labeled.

thank you for your comment and time to help me out with my problem.
 
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Old 11-09-11, 08:30 PM
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Sounds like the pilot orifice is restricted and the flame is not impinging on the tcouple or the pilot is just dirty and the flame has lost direction. Bending the tcouple is not the way to correct. The allen is probably a pressure tap. DO NOT tamper there or try to adjust the main burner. A new pilot may be the easiest way for you to correct the problem. Cleaning an orifice takes some experience so as not to oversize. When you say the furnace is on the floor what do you mean: is it a floor furnace with a grille in the floor or a wall furnace that is installed in the wall with the controls near the floor? OR is it a forced air with the air coming out of floor registers in each room?
Does your gas co make service calls? If yes, try calling them.
 
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