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Old 05-12-2012, 08:00 PM   #1
troidus OP
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Cleaned my furnace, now pilot won't burn right.

I'm trying to schedule a house inspector in preparation for putting the house on the market and thought I'd blow out the furnace with compressed air while I had it opened up to change the air filter. Got tons of rust out of the heat exchanger. After getting it blown out and vacuumed, I went to re-light the pilot and discovered that it's burning at the base of the pilot burner, rather than at the diffuser end up by the thermocouple bulb. Not cool. Now what? (Naturally it won't stay lit, nor would I want it to.) It doesn't appear to be removable separately, and I'm not cracking open a 1" gas line to remove the whole burner assembly. I'm expecting to have to call for service, but I don't want to get flim-flammed.

It's a Lennox G12Q3-82-7. The attached evaporator is a C16-28-1FF.
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Old 05-12-2012, 08:22 PM   #2
DirtyOldMan
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Sounds like you blew a piece of trash up into it. Can you poke it with a small wire and maybe blast it with your air nozzle?
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Old 05-12-2012, 09:05 PM   #3
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I suspect if you take a quick picture with it burning someone may be able to help, there are quite a few knowledgeable heating/AC guys here.

I suspect there is a fitting that you can tighten, but a good pic can help someone who works with these to help you.
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Old 05-12-2012, 09:19 PM   #4
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Unscrew the pilot tube from the gas valve and remove, in the end of the tube where the diffuser is there is a VERY small orifice. Take a small piece of wire and clean it out. Do Not enlarge the hole at all.

You will know its clean when it burns with a stiff flame, when its orange and lazy it will not heat the thermocouple up and keep the gas valve open.
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Old 05-12-2012, 10:43 PM   #5
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I relit it to take photos and it's now burning where it's supposed to. It probably still needs to be removed and cleaned properly. Here are some photos:



The red oval shows where the pilot was burning when I first tried to light it. There's probably an air bleed there and some debris was forcing the gas out at this point, rather than farther up.



Here's a close-up of the diffuser and the thermocouple. Lots of scale buildup.



Here's what the pilot looks like right now. Cropped off the top is the section of flame with yellow tips. I couldn't get the camera in at the right angle to see it.
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Old 05-12-2012, 10:50 PM   #6
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Here's a pulled-back view of the assembly. Looks like maybe a single screw holds the pilot and thermocouple to the burner assembly. Then I'd just have to unhook the much smaller gas line to the pilot. Also, even though this was hit with a flash, you can kinda see the yellow part of the pilot flame.

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Old 05-13-2012, 07:26 AM   #7
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Here is what I see. First lennox does some weird things, most pilots have the flame burning so the thermocouple is above the flame, not to the side. I can see from the marks on the end that it was burning like that before, so nothing has been turned while you were cleaning.
You can remove the pilot assembly by removing the 1/4" nut from the pilot gas tube and the screw that's holding it to the burner assembly. Clean the diffuser piece with a wire brush and knock the scale off,once it is removed look from the line end and see if you see a orifice hole, make sure it is clean,don't enlarge it if it needs cleaned,use a paper clip or a staple something smooth if you don't have wire that small. Sometimes the orifice is in the nut assembly. Remove the same 1/4" line from the gas valve and blow it out. Then reassemble everything and put in a new thermocouple.You can buy a Honeywell universal 24" for less than $5 at most hardware stores. Relight and make sure the flame touches the thermocouple,once red release the button and you should be set.
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Old 05-13-2012, 05:34 PM   #8
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Thanks, everyone. MUCH better. The diffuser was full of crap, so it had to come apart to be cleaned. The gas orifice is a rectangular hole, so no running a wire through it. Good thing it was clean. I ended up replumbing the pilot circuit, because someone had hacked it together sometime in the past. Also, whoever last replaced the thermocouple used an 18", which was too short. The 24" I installed is also too short, really, but at least it doesn't have a sharp 90 bend at the gas valve end like the other one had. And here's the flame:



No more yellow!
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Old 05-13-2012, 05:38 PM   #9
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Oh, and the scale and weak flame might explain why the pilot would squeak every once in awhile. That might also explain why it would sometimes light the burner, then shut it down after 15 seconds or so. I probably should have done this a couple of years ago.

Any idea how old this thing is?
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Old 05-13-2012, 07:13 PM   #10
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Quote:
Originally Posted by troidus View Post

Any idea how old this thing is?
What's the s/n ?

Mike
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Old 05-13-2012, 07:50 PM   #11
troidus OP
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Quote:
Originally Posted by cogswell View Post
what's the s/n ?

Mike
5891b10004
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Old 05-13-2012, 10:12 PM   #12
Walterxr650l
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Quote:
Originally Posted by troidus View Post
Any idea how old this thing is?
If it is a furnace with a standing pilot, my guess would be 30 plus years.

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Old 05-13-2012, 10:42 PM   #13
troidus OP
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Quote:
Originally Posted by Walterxr650l View Post
If it is a furnace with a standing pilot, my guess would be 30 plus years.
Nope. I looked it up online, and if the source is accurate, it was built in February, 1991. 5891b10004
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Old 05-14-2012, 05:33 AM   #14
Cogswell
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Originally Posted by troidus View Post
Nope. I looked it up online, and if the source is accurate, it was built in February, 1991. 5891b10004
Glad you found it, most manufacturers code the build date into their serial numbers.

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