pilot won't stay lit

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Old 03-10-13, 06:24 AM
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pilot won't stay lit

I have a Hamilton, natural gas furnace. The pilot lite won't stay lit. It's done it numerous times. I put a new thermocoupler on it for the second time this year, and it's just not stayin lit. I've cleaned around the pilot lite tube a couple of times. I have a good, solid, blue flame. It just won't stay lit, even when I'm pushin down on the plunger thing and slowly releasing it now. Why won't it stay lit ?
 
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Old 03-10-13, 06:58 AM
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If you have a good pilot flame and new thermocouple then it is the gas valve that is at fault.
 
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Old 03-10-13, 07:30 AM
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Is there anything that I can do with the valve to clean it or anything ?
 
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Old 03-10-13, 08:45 AM
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The gas valve is replaced. There are no user serviceable parts inside of them.

Also....make sure the thermocouple is fully in the flame.
 
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Old 03-10-13, 09:23 AM
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I'm pretty sure the thermocoupler is in the flame good, it's hard to see with a bracket right between it and my line of sight, but the thermocoupler does wiggle a little, and I can see it moving the flame around when I do this. I put a new ferrule in it with the new thermocoupler, so it should be as tight as needed. I got the pilot lite to stay lit just now, but it seems to go out after the burner kicks on, or when it shuts down. Its done this probably 5 times this winter. Hard to get it lit, and sometimes it will just go out,... not a windy day either.
 
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Old 03-10-13, 09:47 AM
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The pilot solenoid in the gas valve is weak.
Thermocouples generate electricity directly from heat. They take advantage of an electrical effect that occurs at junctions between different metals. For example, take two iron wires and one copper wire. Twist one end of the copper wire and one end of one of the iron wires together. Do the same with the other end of the copper wire and the other iron wire. If you heat one of the twisted junctions with a flame and attach the two free iron wires to a volt meter, you will be able to measure a voltage.

In a standing pilot system, one of the junctions of a thermocouple is sitting in the pilot light's flame. The electricity that is created runs to a small electromagnetic valve and holds it open. If the pilot light blows out, the thermocouple quickly cools off. It stops generating electricity and the valve closes.
 
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Old 03-10-13, 09:54 AM
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So, I need a valve,... where is the best place to get one ? I can shop online. Also, I would like to get a ballpark figure of how much longer this old furnace might last,.. can I tear it apart and say, check the heat exchanger to see if it looks good, and what should I look for ?
 
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Old 03-10-13, 10:07 AM
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A gas valve should really be done by a professional that has the proper tools to ensure the gas pressure is set properly for your furnace.

Anything with a standing pilot is fairly old. Average life for a furnace in my area of the country (I see you are also from IN) is 15-20 years. Checking the heat exchanger visually should be done by a trained eye that knows what to look for. Cracks can be gapping and huge or tiny and hard to notice. If you have not had the unit serviced recently it would be a good idea to do so.
 

Last edited by hvactechfw; 03-10-13 at 10:52 AM.
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Old 03-10-13, 10:33 AM
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Thank you for all you time and very knowledgable assitance !
 
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