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My furnace fan was running constantly and the heat would not start. Through some research I discovered this was likely due to a faulty limit switch in my furnace.

I don't have the exact model of my furnace but it is a Lennox G20/G20R/G23/G26 Elite series with Honeywell VR8200 controls.

I found found a limit switch that I thought was the culprit, part number 18J3701, but it completely passed all testing I did on it. I followed the circuit more and found another limit switch and identified it as the culprit. To be clear, that P/N switch was NOT the culprit; it was in the air chamber and had a set point of 205 degrees F and reset point of 175 degrees F.

The second switch (not working) was right by the burner and I cannot find any information on it. I checked the burner and heat exchanger and surrounding parts and I did not see any damage or evidence of overheating, so I'm sure it's just a switch failure and nothing more. The switch is showing as an open circuit with my multimeter and when I test by removing the switch from the circuit and only have the other switch in place, the furnace works fine.

I verified a couple cycles of the furnace, then I turned everything off. I won't take chances letting it run without the switch. Right now I have the breaker to the furnace OFF, as I don't want it running without all the safety mechanisms in place.

It has black plastic packaging and faint numbering on the side (6063 J9815. Where I can I find a replacement for this? I found a similar switch but since I don't know the specifications, I don't know if this one will work or not - I don't know if it will trip at the right temperature. Obviously, I don't want to take chances, I want to be sure of what I get, but finances are really tight and I can't afford a maintenance visit right now.

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  • I'm not sure why this question didn't get more attention, but I'm in the same boat. My limit switch has a part number and a large 15 on it, but I've been unable to find a replacement, even by furnace model number. A guide for determining specifications and finding a compatible replacement would be invaluable.
    – isherwood
    Dec 4, 2023 at 13:46

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16 min ago : A guide for determining specifications and finding a compatible replacement would be invaluable

quickest way I can answer your request is - does there need to be a specification list in order to find replacement shoe laces for your shoes, so you can find a compatible replacement? I mean there's all different kind of shoes (boots, sneakers, dress shoes) and then there's different sizes, colors, features, waterproof or not, the list goes on and on. For a residential furnace a limit switch is... a limit switch, like shoe laces are like shoe laces.

To answer your subject question - many places; amazon obviously, supplyhouse, numerous other mail order places, and then any local place that sells furnaces (i.e. plumbing supply places). Your 2nd and 3rd sentence, I sorta stopped reading there, your research was faulty, that's not how a limit switch works. But I did read all your text, my suggestion would be to (a) find the correct brand/model/serial then (b) go the old RTFM route and see what the diagram calls out this particular switch to be, rather than guess.

This was Asked 3 years, 2 months ago and you had stated I want to be sure of what I get, but finances are really tight and I can't afford a maintenance visit right now. After that much time of build back better you surely should have better finances by now and be able to afford a maintenance visit. If not then consider my recommendation. Then again, you should be replacing that gas furnace with something all electric, fossil fuels are bad.

and you don't look at digikey or mouser for replacement residential furnace parts.

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    There's a lot of irrelevant commentary here and some rather vague advice. I suggest reformulating to 1) not reference my comment, which isn't really important, 2) not answer a question with more questions, 3) ignore question age, 4) not give irrelevant moral advice, and 5) be more specific about what aspects of the switch are important. I've searched all 6 numbers on mine, along with the furnace model, and can't find a confident solution.
    – isherwood
    Dec 4, 2023 at 14:30
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    In short, this answer doesn't help at all.
    – isherwood
    Dec 4, 2023 at 14:32
  • you don't start off a request for help with first stating I don't have my exact model of furnace. the furnace fan running constantly with the burner [heat] not turning on is not how a limit switch works. you're not going to find a replacement residential furnace control at digikey or mouser. My irrelevant commentary was in response to the original poster's statement of finances are really tight and I can't afford a maintenance visit. As well as being climate conscious.
    – ron
    Dec 4, 2023 at 14:40
  • and he also said I don't want to take chances, I want to be sure of what I get. So a maintenance call by someone qualified to work on his unit would be the best course of action, surely his finances ought to be better by now. Please elaborate on how anything I said was irrelevant commentary.
    – ron
    Dec 4, 2023 at 14:48
  • the really comical thing is, all you have to do is get the serial # of the furnace with the model number, go to a local supply place and simply ask. Or online chat with supplyhouse. I don't think online chat with digikey or mouser will be successful.
    – ron
    Dec 4, 2023 at 14:57

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