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Lennox Gas Furnace that turns on and shuts off in minutes

The unit will turn on and run fine for a few minutes then shut off. It won't immediately turn back on, almost as if it has to cool back down first. Any ideas?

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  • jros5 Nov 19, 2008

    I have the very same issue and I'm troubleshooting it now. What's interesting is that it'll sometimes fire and stay on for a long time. I replaced the thermostat upstairs on the wall and it seemed to work overnight but in the morning, same problem. I could get it to kick on with the thermostat, but it would only fire for about 2 seconds and stop. It would cycle again and fire after 7 seconds, failing again after 2 seconds (it would repeat this until I killed power to the furnace completely).



    The unit has been operating normally now for about an hour, so the house is warming up. When it's warm enough to give me time to mess with it, I plan on trying to eliminate a short in the wiring from thermostat to the furnace control board. I will do this by jumping a wire on the control board between the red and white wires to complete the circuit, as the thermostat would. If it operates flawlessly and stays fired when hot or when cold, then it's either a short in the wiring or something with the thermostat (doubtful as I replaced that already...*however* the first replacement was broken out of the box--I had to return it for another).



    I'll update with my progress...

  • richardsdm Feb 02, 2009

    Have a Lennex/Armstrong gas furnace. Approx. once a week furnace will try to cut in and then quit after a few seconds. Get a flash fault code of 3 - Pressure switch open with inducer on. What does this mean, what is the likely cause. Furnace is only 3 years old. I can turn off power to furnace and turn back on and it is ok for a few more days. Solutuions???

  • aocomp
    aocomp Dec 02, 2013

    there are two gas circuits, pilot and main.

  • Dan Fidoe
    Dan Fidoe Mar 05, 2014

    Drain line. Mine was clogged. Fixed the issue.

  • Dan Fidoe
    Dan Fidoe Mar 05, 2014

    Clogged Drain Line. Fixed my issues.

  • Dan Fidoe
    Dan Fidoe Mar 05, 2014

    http://www.youtube.com/watch?v=maZ4JskGj...

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After troubleshooting like mad, I found that the flame sensor (rod that sits within the flame) was fouled with carbon on the surface. I believe this shields the rod from proper heat detection and the sensor reports that there is no flame and to shut off the gas valve to avoid explosion. Once I pulled out the rod and cleaned it with a wire brush, I have no problem whatsoever--fixed.

Posted on Nov 20, 2008

  • lander guy Nov 11, 2010

    If you don't have a wire brush, try sandpaper. IT worked for me. I have nothing but warm thoughts of you. lol Thanks.

  • godiva1004 Dec 17, 2010

    I have a "lovely" Lennox furnace that does the same exact thing and after calling out a repair person and standing next to him to watch what he did, he used sandpaper to scrub the carbon off the flame sensor rod and put it back in place. He told me some repair places will tell you you need to buy a new one (which is expensive) but they are notorious for doing this every couple of years so just clean it yourself until you absolutely need a new one. It seems nothing is built like it used to be. :(

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I have a Lennex Gas Furnace, It turn on and stay on for about 20 mins then turns off. You can hear the electronic ignition trying to stay the furnace but nothing sometimes after four or five tries it will come back on, but it never warms my house to the temp. set.

Posted on Jan 07, 2011

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SOURCE: The unit will turn on and run fine for a few

The ignitor will light, the blower will start up and run for a few minutes and then the system will shut down, and the blower will continue to run and cool down. The ignitor is not working properly, the ignitor has carbon build-up and need to be removed, cleaned all the black carbon from the ignitor with a little piece of sand paper and replaced, turn the heat back on and this should correct the problem.

Posted on Dec 14, 2009

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Posted on Jan 02, 2017

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