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Old 02-26-2011, 12:44 AM   #1
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Lennox 80UHG doesnt blow heat


Hi...
I don't know anything about furnaces, so bare with me. Current house temp is 60 and we are freezing, can't get anyone out here asap, figured I'd drop in here to see if there are some easy fixes.

I have thermostat usually always set to 66, heaters been working fine forever, this morning I heard it click'...something starts running, but the fan never starts blowing (I dont think) nor do I hear the usually tick tick FLAMING WOOOSH sound.

Any tips?

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Old 02-26-2011, 08:34 AM   #2
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Lennox 80UHG doesnt blow heat


Look at the diagnostic lights and compare the flashes to the label on the door. Probably locked out in watchguard mode. Shut the power off, clean the flame sensor and try starting again.

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Old 02-26-2011, 11:45 AM   #3
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Lennox 80UHG doesnt blow heat


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Originally Posted by Marty S. View Post
Look at the diagnostic lights and compare the flashes to the label on the door. Probably locked out in watchguard mode. Shut the power off, clean the flame sensor and try starting again.
56 this morning in here! yikes, in so cal! (lovely weather proofing on this house I see).
Just crawled up in attic, I see 2 green LED's flashing, together, don't remember seeing a diagnostic panel, but will check again.
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Old 02-26-2011, 12:17 PM   #4
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Lennox 80UHG doesnt blow heat


should be on the blower door, may be on inside of the door. were they flashing alternately or simultaneous? flashing fast or slow? Did you turn power off and back on? this will reset the control and may get you temporary heat. We do need the diagnostic code to help figure out the cause to come up with a repair though. It would also help if after you reset the control if you stay and watch a ignition sequence and post here what happens.... I would start with cleaning the flame sensor though. or
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Old 02-26-2011, 12:28 PM   #5
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Lennox 80UHG doesnt blow heat


Found the sensor, pulled out and used steel wool to clean it. Corrosion was not too bad though?
Anyways, put it back in, still same thing: the thermostat clicks some sort of action happens at the furnace, but the big blower NOR flame come on.

The lights flash together with about 1-1.5 second gaps between I'd say?

Heater did not work 2 years ago, guy charged me $800 for a new circuit board or something? I don't have $800 right now, let alone $8, so I was hoping for an easy fix
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Old 02-26-2011, 12:41 PM   #6
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Lennox 80UHG doesnt blow heat


i take that back on the LEDs, they are rapidly flashing, together when its trying to start. I don't know the proper startup phase so forgive my terminology. There is a humming coming from the furnace, but nothing is 'firing' nor is the big main fan blowing. I can get the fan/blower? to go if I put the thermostat to ON vs AUTO, but no heat is happening. Maybe try cleaning the sensor again? doubtful I guess.
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Old 02-26-2011, 12:43 PM   #7
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Lennox 80UHG doesnt blow heat


did you find the diagnostic legend?
that sounds like a stat problem, check for batteries, if your stat has them, then replace them.

otherwise remove wires from R and W and twist together, this should change the flash at the furnace.

MANUAL see page 8 for diagnostic information
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Old 02-26-2011, 12:51 PM   #8
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Lennox 80UHG doesnt blow heat


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did you find the diagnostic legend?
that sounds like a stat problem, check for batteries, if your stat has them, then replace them.

otherwise remove wires from R and W and twist together, this should change the flash at the furnace.

MANUAL see page 8 for diagnostic information
diagnostic legend, that is what you linked to at the bottom, right?
and 'stat' you mean thermostat on the wall right?
remove wires from where?
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Old 02-26-2011, 12:58 PM   #9
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Lennox 80UHG doesnt blow heat


this is probably the problem, see if the humming is coming from here. if it is, the motor is stuck. if this is not running during call for heat then check for 120V ,with a multimeter, to the motor.
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Old 02-26-2011, 01:01 PM   #10
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Lennox 80UHG doesnt blow heat


Both lights fast flashing means the thermostat is calling for heat. The inducer motor should come on next. Does it?
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Old 02-26-2011, 01:01 PM   #11
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Lennox 80UHG doesnt blow heat


Your image did not show.

And the diagnostic tells me everything is fine (green lights) clearly everything is not fine.
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Old 02-26-2011, 01:03 PM   #12
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Lennox 80UHG doesnt blow heat


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Both lights fast flashing means the thermostat is calling for heat. The inducer motor should come on next. Does it?
Like I said in the original post, I know nothing about furnaces, so I don't know what an inducer motor is. But also as I said, the thermostat 'clicks' and the furnace starts something, perhaps the inducer motor? all I know is I don't hear the usual BURNER sound NOR the big fan/blower that spits out hot air around the house. Something is turning on in furnace, just no fire or blower (blower I think is name eh? of the big fan that blows the actual hot air).
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Old 02-26-2011, 01:06 PM   #13
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Lennox 80UHG doesnt blow heat


Is the ventor fan that pushes the smoke to the chimney running. If so carefully remove the tube from the pressure switch hose where it attaches to the collector box/furnace (NOT the switch itself) and poke a paper clip/small bit thru that hole. It should be giving you a open pressure switch code but you are having a hard time reading it. Look at the pic in here
http://www.hvacparts.ca/LennoxPDF/80UHG.pdf
the inducer is the fan at the top and the pressure switch is below it.
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Old 02-26-2011, 01:09 PM   #14
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Lennox 80UHG doesnt blow heat


The inducer is a little motor where the flue hooks up. It comes on and closes a pressure switch if the flue is clear. Check the flue for a dead bird.

If the pressure switch doesn't close then the furnace will not continue the start up sequence.
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Old 02-26-2011, 01:11 PM   #15
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Lennox 80UHG doesnt blow heat


inducer.... again go to manual see page 8 for diagnostic code and below that is the sequence of operation. Page 25 starts diagnostics

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