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Old 10-26-2009, 08:24 PM   #1
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Lennox furnace - no heat


My Lennox furnace just quit on me.

I only used it a few times this year, but it suddenly quit working.

When I turn the heat on it will kick on for a few minutes, but then it stops.

I replaced the filter and cleaned the flame sensor.

Still nothing.

Any ideas?

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Old 10-26-2009, 08:30 PM   #2
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Lennox furnace - no heat


Go look at the board, and post back with the code that it is flashing, then wait for someone to chirp in.

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Old 10-26-2009, 08:33 PM   #3
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I should have posted that - the codes are flashing normal.

Is it possible that the gas is not getting ignited?
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Old 10-26-2009, 09:36 PM   #4
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Update - there was an HVAC guy at work today who told me I could call him with any questions. I just got off the phone with him - he told me the igniter should be glowing red once the system starts up - but it was not. He said it’s a common failure item and to replace it tomorrow.

Only one thing....he said I could ohm it to make sure it was bad. He also said I could check the lead going into it to make sure it was sending out power.

Ohmed it - there is continuity. Shouldn't it give me no reading if it’s dead?

110 volts are coming out of the igniter power for a couple of seconds - means the board is good...correct?

Finally - I looked at the trouble codes and there is one for "burners failed to ignite".....shouldn't I have gotten that code?

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Old 10-26-2009, 10:31 PM   #5
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Lennox furnace - no heat


You want to read ohms not continuity.
Do you see any visable cracks on the ignitor?

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Old 10-27-2009, 07:37 AM   #6
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No cracks, but it has turned white.
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Old 10-27-2009, 07:53 PM   #7
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Replaced the ignitor and thats not it.

When I unplug the ignitor I can get a reading on the power source for a few seconds. Since the circuit is not complete, it shuts off and gives me the incomplete circuit trouble code.

I tried to stick the meter into the wire harness while the unit is running to see if I'm getting power - no reading. I thought perhaps I'm not making good contact, but the harness is pretty open and I'd have to assume I'm making good contact.
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Old 10-27-2009, 08:12 PM   #8
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Post the model and serial # of the furnace. I am a Lennox tech.
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Old 10-27-2009, 08:20 PM   #9
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Model G40UH-368-090-02
SN 5801F 41160
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Old 10-27-2009, 09:02 PM   #10
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Where did you get the igniter? A Lennox dealer? Cozyparts.com ? The G40 uses a different igniter than the G50. They also work off a reduced voltage, 83 volts I believe. I'll post you a service manual for it. I got to go now.http://tech.lennoxintl.com/PDFs/0006j.pdf
Back tomorrow.
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Old 10-27-2009, 09:17 PM   #11
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I got it from a local parts store - it is an 80 volt ignitor. Is that not correct?
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Old 10-28-2009, 02:32 PM   #12
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I was told by a tech today that I need to find out if the pressure valve is good. He tried to describe how to short it our or suck on it, but I couldn't understand him. Can anybody elaborate?
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Old 10-28-2009, 05:58 PM   #13
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The pressure switch is NOT to be sucked on or it gets damaged. If it does not close the board will show an error code. Lets start in the BEGINNING. Does the thermostat start the furnace and does the ventor fan to the chimney run?
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Old 10-28-2009, 06:04 PM   #14
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Quote:
Originally Posted by yuri View Post
The pressure switch is NOT to be sucked on or it gets damaged. If it does not close the board will show an error code. Lets start in the BEGINNING. Does the thermostat start the furnace and does the ventor fan to the chimney run?
The thermostat does start the furnace.

Ventor fan to the chimney - do you mean the inducer fan, or the one on the bottom of the unit?
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Old 10-28-2009, 06:05 PM   #15
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The one above the burners and pushes the smoke to the chimney.

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