 ZupperPremium
join:2002-12-28
Novelty, OH | Furnace pilot out twice The pilot light on my furnace has been out twice in the last week. I think this is indicative of a failing thermocouple. However, I am not sure how to find the right replacement part.
The furnace is a Lennox, model G12Q3-137.
The thermocouple (flame sensor) has a long copper line that connects it to the gas control valve. The few things I have found online do not look like that. And this model furnace seems to be old enough that there is not a lot of information or cross-references.
Anyone have a good idea of where to look?
Thanks. |
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robbinPremium,MVM
join:2000-09-21
Leander, TX
kudos:1 | Should be able to buy a thermocouple at the local big box. |
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rfnutPremium
join:2002-04-27
Fisher, IL | reply to Zupper
Sounds like it is a standard thermocouple. Sold in different length. Any one long enough may work. |
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ZupperPremium
join:2002-12-28
Novelty, OH | reply to Zupper
Oh, OK. So, besides the length, there are no other specifications to consider that would affect compatibility? |
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 jjoshuaPremium
join:2001-06-01
Scotch Plains, NJ
kudos:3 | Output voltage would be a big one. |
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 Lurch77BBR BullyPremium
join:2001-11-22
Oconto, WI
kudos:4 | reply to Zupper
Thermocouples you buy these days are universal, so they will work with the screw in, push in, or clamp in mount. Got a home cheapo by you?
»www.homedepot.com/buy/honeywell-···OPqXFW8A
Otherwise most hardware stores will have them too. Mount the thermocouple then gently uncoil and hook it to the gas valve. Tighten it to 1/4 turn past finger tight. Don't kink the lead. |
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TexPremium
join:2012-10-20 | reply to Zupper
That's a pretty old furnace (20+ years old). Other than the thermocouple failing, you might want to check the heat exchanger for holes and/or cracks. The older the furnace, the better the chance the heat exchanger could have a hole or crack in it, perhaps somewhere around the burner where the pilot assembly is mounted.
One way to check the heat exchanger of your particular furnace for holes or cracks is to turn on the blower only and use a fireplace match or a lit twisted up piece of paper, placing the flame around the openings of each burner chamber and watching the flame to see if it moves around or even goes out.
Do you have your furnace checked before each heating season? |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
 ·TekSavvy DSL
| reply to Zupper
said by Zupper:The pilot light on my furnace has been out twice in the last week. I think this is indicative of a failing thermocouple. You could try cleaning the tip gently. If you have a DMM that can measure accurately in millivolts, place the tip in any flame and see if open circuit voltage is at least 22mV after cleaning.
Pilot flame goes out below 20mV. That could be because of dirty or faulty thermocouple ... but it could also be because the pilot flame is not completely touching the tip. If you are comfortable, you could adjust the flame abit.
said by Zupper:The few things I have found online do not look like that. Can you post a photo of the current thermocouple? If it is a straight short tip, most probably it is the same one used in my old York furnace. |
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 jack bGone FishingPremium,MVM
join:2000-09-08
Cape Cod
kudos:1 | reply to Zupper
Thermocouples do go bad, changing one is usually not too challenging. In some cases you may have to remove the main burner to get the thermocouple out of it's mounting bracket.
Some things to consider: If there is insufficient gas pressure the pilot flame will shrink causing it to drop out.
A blockage in the pilot burner gas orifice or primary air inlet can also cause the flame to become soft and unstable, making it easy to extinguish itself.
If the heat exchanger is cracked that can cause the pilot flame to go out repeatedly.
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 Chuck22Premium
join:2003-11-10
Salt Lake City, UT
kudos:4
 ·Comcast
| reply to Zupper
Had similar problem with ComfortMaker furnace early this winter. Pilot would not stay lit. HVAC tech came and replaced thermocouple. The next week same problem: pilot went out three times during the week. A different HVAC tech came and found the problem was the main valve. Replaced the main valve assembly and pilot problem went away.
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amicitia sine fraude |
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ZupperPremium
join:2002-12-28
Novelty, OH | said by Chuck22: A different HVAC tech came and found the problem was the main valve. Replaced the main valve assembly and pilot problem went away.
So how did he "find" the problem was the main valve? Or was it more an educated guess, since the thermocouple didn't fix it? I am just wondering if there is some diagnostic work I could do.
I am leaning on just doing the thermocouple, since I can do that myself for relatively cheap. I haven't ruled out the valve, so if it happens again, could then have that replaced. |
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Chuck22Premium
join:2003-11-10
Salt Lake City, UT
kudos:4 Reviews:
·Comcast
| said by Zupper:So how did he "find" the problem was the main valve?
I recall that he mentioned that in most cases when replacing the thermocouple does not solve the problem, the issue is with the main valve. If I remember correctly, he also tapped (pounded on) the valve and got it to work one time, and said something about a sticking valve needed replacement.
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amicitia sine fraude
(friendship without deceit) |
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