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Old 12-11-2011, 06:06 PM   #1
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Lennox 80UHG not firing


Hi!

I am new to this group and I don't know much about the furnaces.

The heating from one unit stopped working. I read the manual and got some idea of the unit. I googled and found this great site. Learnt a lot in the past few days.
1. Cleaned the ignotor accidentally thinking it is the flame sensor.
2. Cleaned the flame sensor

Still no heat

When I press and hold the door switch (after opening up all the covers) I hear the unit click and come on. The blower seems to come on.

The diagnostic light 1 and 2 flash quickly for a second or two and then immediately diag 1 starts slow flashing and diag 2 on (no flashing). This says Primary limit open etc..

The trouble shooting says the inlet or outlet air may be blocked.

Now I don't know where this is located and how to remove it. Is it the white pipes on the side? There are 2 of them.

I would appreciate any help please. I thought I will try this before calling the tech.

My unit is 13 years old. Ablsoutely no problem till now.

thanka a lot for your help.

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Old 12-11-2011, 06:10 PM   #2
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Lennox 80UHG not firing


limit shuts down unit in high temp ..check filters ....also may have dirty a-coil for a/c or the blower may not be comming on...

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Old 12-11-2011, 11:42 PM   #3
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Lennox 80UHG not firing


By filters do you mean the 20 x 20 x 1 home air filters through which the air gets sucked in ? or Is there a separate filter at the unit?

They look really dirty. I will change them and let you know what happens.

The blower actually comes up and continues running. But nothing happens after that. The ignitor does not heat and turn orange. The burners do not kick off.

Thanks for the quick response.
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Old 12-12-2011, 04:08 PM   #4
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Lennox 80UHG not firing


You may have ruined the ignitor by cleaning it. It is fragile and can be affected by the oil in your skin. It may have to be replaced.
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Old 12-12-2011, 06:44 PM   #5
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Lennox 80UHG not firing


Replaced all the filters (14 x14 ) and 20 x 20 filters. Still no heat.

Help please.

How do I clean the inlet air and the outlet air? Can someone point me to where they are located please? All I see is the big silvery pipe.

I will also replace the ignitor and see if it helps. Is it better to try what the trouble shooting section in the manual says first ?

Please let me know.

thanks

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Old 12-12-2011, 07:27 PM   #6
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Lennox 80UHG not firing


Inlet air on yours is just through the louver front door. If any modifications were done in the furnace vacinity since last heating season, try opening a door, as appropriate, to let unit get more air. (Not likely.) Outside air would be vent to a chimney. This means an animal, debris or such got in and is blocking exhaust. (Possible?)

See this: http://www.lennox.com/pdfs/manuals/L...UHG_Manual.pdf



In first sketch, the combustion fan is at the top. It should come on first. Check that it's spinning and not jammed/seized or broken. The little rubber hose from it to the big round silvery disk (the pressure switch) should be carefully removed and examined for leaks or cracks.It should not have anything in it. If it looks gunked up at either end, clear with an opened paper clip.Reinstall.

Your unit should have 20 x 20 x 1 filter. Maybe remove the 14 x 14. Try removing 14 filter. You may be overfiltered and limiting air flow. Try this first.

Report back.

Thread in another forum: http://www.doityourself.com/forum/ga...itch-code.html

Last edited by diyorpay; 12-12-2011 at 07:44 PM. Reason: add
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Old 12-12-2011, 10:06 PM   #7
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Lennox 80UHG not firing


Thanks DiyOrPay

Will try it and let you know.
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Old 12-13-2011, 10:47 AM   #8
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Lennox 80UHG not firing


Quote:
Originally Posted by diyorpay View Post
Inlet air on yours is just through the louver front door. If any modifications were done in the furnace vacinity since last heating season, try opening a door, as appropriate, to let unit get more air. (Not likely.) Outside air would be vent to a chimney. This means an animal, debris or such got in and is blocking exhaust. (Possible?)

See this: www.lennox.com/pdfs/manuals/Lennox_80UHG_Manual.pdf



In first sketch, the combustion fan is at the top. It should come on first. Check that it's spinning and not jammed/seized or broken. The little rubber hose from it to the big round silvery disk (the pressure switch) should be carefully removed and examined for leaks or cracks.It should not have anything in it. If it looks gunked up at either end, clear with an opened paper clip.Reinstall.

Your unit should have 20 x 20 x 1 filter. Maybe remove the 14 x 14. Try removing 14 filter. You may be overfiltered and limiting air flow. Try this first.

Report back.

Thread in another forum: http://www.doityourself.com/forum/ga...itch-code.html
I tried the following as you suggested:

I removed the hose. Looked clean at both ends. Blowed air on one end and felt it on the other end. Put it back and turned the unit on. The combustion fan spun for a little while and stopped.
I tried it a couple of more times. But both these times it would try to spin (one slow revolution) and stop. I tried to spin it with a screwdriver. It would spin a few revolutions and then stop.

I checked the other link you sent me. They are talking about very similar issue. Turned out to be a pressure switch issue in that case. Do you think mine is the same. They talk about flicking the pressure switch. Don't know how to do that. they also talk about bypassing pressure switch to see if it is the issue. Don't know how to do that either.

Please let me know.

Thanks again for your help.
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Old 12-13-2011, 08:03 PM   #9
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Lennox 80UHG not firing


Limit switches look like this:

http://www.google.com/products/catal...ed=0CH0Q8wIwAg

I would gently tap the back of any switches with the handle of a screwdriver to see if 'hung up'. If it comes lose and furnace starts, might be better to replace anyway.
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Old 12-14-2011, 09:00 AM   #10
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Lennox 80UHG not firing


Thanks Diyorpay

Could not stand wife complaining anymore. Called in a HVAC expert. With all your postings and expert suggestions I could at least converse with him intelligently. He checked the pressure switch and everything else. when he shaked the 12 point plug (the one that leads to the Press switch, gas valve etc) which attaches to the control board the unit started working. It still looks jerky. He is saying the control board is the issue (installed : 425 $). He said that I could replace it myself. Not sure about that. what if it is the 12 point plug?

Thanks for all your help.

Fantastic website. Learnt a lot during the past few days.
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Old 12-14-2011, 09:21 AM   #11
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Lennox 80UHG not firing


If '12 point plug' is just the harness of wires to the control board, check them carefully. Looseness and corrorsion etc, anything unusual. Could have been just due to vibration?

If tech didn't unplug and replug harness, do it. Check any wires that might be twisted under a plastic cap. All with power off.

If you want to, take a pic of board for your reference (or draw a sketch) and remove wiring to control board. Remove it and check front and back for burn marks or obvious damage like a crack in solder. Up to you if you want to replace. I did it once. My local plumbing shop hates White Westinghouse and I replaced with a Honeywell. Instructions with board explained which wires went where. Not difficult to do if that is indeed the part that solves the problem.
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Old 12-14-2011, 01:19 PM   #12
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Lennox 80UHG not firing


Will check that. The unit is working continously since yesterday evening (knock wood). Next time it fails I will try the new control board like you suggested.

thanks again
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Old 12-14-2011, 01:29 PM   #13
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Lennox 80UHG not firing


fingers crossed

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