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Old 11-19-2009, 03:02 PM   #1
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Lennox 80MGF - No Heat


Hello all, I have a furnace that will not provide heat. Here is what it happening at start up after resetting the furnace and turning up the heat... We get the call for heat, the draft blower kicks in and pressure switch actuates. (The pressure switch checked good using a meter during this also). Then the gas valve keeps clicking loudly like it is cycling on and off over and over again. Note the igniter is not on during any of this. This clicking continues until the unit locks out. Anyone have any ideas on a probable cause and isolation procedure?

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Old 11-19-2009, 05:32 PM   #2
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Lennox 80MGF - No Heat


The clicking from the gas valve is the control board sending 24 volts on and off when it shouldn't be. New circuit board will fix you right up.

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Old 11-19-2009, 07:15 PM   #3
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The igniter should glow red first or the spark on first and then the gas valve gets energized. Try Cozyparts.com for Lennox parts. Lots of their boards are retrofits so you have to be VERY careful and follow the instructions EXACTLY and pay attention to the model# completely as it has a series # built into it and that means a LOT.
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Old 11-20-2009, 06:57 AM   #4
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Lennox 80MGF - No Heat


Thanks Marty and yuri, I purchased a board from a local Lennox dealer. The new board seems to be defective. I have no power to the transformer, thus, no power no 24v to the board. The new board is an EGC1 but is suppose to work to replace an EGC2. The board is getting power, but the 120VAC Is not avail at the TX terminal. I considered taping into 120 buss but did not as I was uncertain how it might affect the board. Any ideas?
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Old 11-20-2009, 07:22 AM   #5
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Lennox 80MGF - No Heat


The new board has a warranty, I'd return it. You can piggyback L1 and tx to get through the weekend.
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Old 11-20-2009, 03:57 PM   #6
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Lennox 80MGF - No Heat


Post the complete model # so I can check into the specs for it.
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Old 11-20-2009, 06:54 PM   #7
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Lennox 80MGF - No Heat


Hello All, When I got off work today I went back to the Lennox dealer and the agreed to replace the board. I am getting ready to change it out again. The service manager stated he has never heard of this board having this problem. The replacement board is another 17W82 kit for an 80MGF-75A-9 furnace. Wish me luck.
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Old 11-21-2009, 11:20 PM   #8
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This evening, my Lennox 80MGF started doing the same thing. . . the gas valve clicks loudly, the ignition sequence shuts off and the diag lights both flash (the code says the control board is faulty). I think this is the same problem Thome was having earlier this week.

I'll be buying a new control board on Monday, but to get me through the weekend, Marty, can you explain in more detail what you mean by "you can piggyback L1 and tx"? Will that procedure work with the existing faulty control board, or is that a way of rerouting the power from Thome's old board to his defective new one?

Thanks!

--Cold in Boise
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Old 11-21-2009, 11:47 PM   #9
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Lennox 80MGF - No Heat


That was to get power to the transformer since his new board was not working. It will not help you. Sorry but there is no option for yours except wait for the new circuit board.
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Old 11-22-2009, 08:51 PM   #10
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Lennox 80MGF - No Heat


New board is in and furnace is working great! Thanks for your help!
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Old 04-06-2010, 10:54 AM   #11
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I've had this same issue with my furnace over the last winter season. I'm very glad to have found this posting thread as I was sure it was the gas valve that was the problem.
I found an unusual (and temporary) workaround that has bought me some time. My Lennox 80MGF does the same thing, but only when the temperature in the heater closet is too low. At first, setting the thermostat temperature a little higher so that it never got too cold in the heater closet worked, but the problem got progressively worse through the winter. Now if I put a space heater in the closet for five minutes in the morning when the heater is first coming on for the "Wake" cycle, it will start. Otherwise it repeatedly starts and stops with a child-waking clunk. I think this must mean that there is a bad contact on the board somewhere and that thermal contraction causes it not to work. That is a hallmark of a faulty solder connection somewhere on the control board.
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Old 04-01-2011, 12:30 PM   #12
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Lennox 80MGF - No Heat


I have problem with heating during My furnace operation...

Start from begainning...

1. combuston air blower starts
2. after 15 sec(~) flame starts... and just within 2-3 second flame stops..(this is the problem)
3. again after another 15 sec~ flame starts and it stops within 2-3 secs... but not countinous flame runs till call for Air Blower to starts... cycle interept in between? and no any error code by shows led ( shows Heat Mode On) The gas valve keeps clicking loudly like it is cycling on and off over and over again. Note the igniter is "ON" during any of this.

This problem will fixed .. if i shut off main power for 2 min. and start again. but i cant not do every one hour when furnace starts to match up setting for heat.. Hope you understand..

Now Guide me what is the problem? and why its doing like that? and what should i do? Thanks

Furnace details
LENNOX (14 YRS OLD)
Heating Units - Gas DSI
80MGF
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Old 04-01-2011, 01:32 PM   #13
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This sounds very similar to the problem that I had. Eventually I solved it on my own by ordering a replacement control card from cozyparts.com. The part number was 17W82, and it cost $125 in August 2010. It looks like the price has gone up a little, but not too much:

http://cozyparts.com/lennox-parts/Se...?Keyword=17W82

Compare that with the many hundreds a tech will charge to come to your home and diagnose/repair.

They also have the part manuals online, too, which is a big help.

The wiring was a little different from the old card, so I was careful to write down all of the connections and label the wires. Over all it took ~30 mins to swap out the control card, and I haven't had any trouble with the heater since that time.

I suspect that there was a broken solder joint somewhere on the card that provided intermittent connection. In my case, it was temperature related. It could also be interrupted by vibrations when the main blower turns on, too.
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Old 04-02-2011, 11:45 PM   #14
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It may be just the flame sensor. The board needs a certain amount of dc micro amps from the flame sensor in the burner compartment, if you clean the flame sensor with emery cloth or scotchbrite and clean the burner in front of the flame sensor also because the amperage travels through the flame to ground. If every thing is clean and the problem still continues it probably is the board not sending enough voltage to the flame sensor (like pdxsk) if you know the voltage the flame sensor needs you can measure it with one meter lead from the flame sensor wire and the other lead to ground.

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