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Furnace and Thermostat questions (Lennox G20)

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  • Furnace and Thermostat questions (Lennox G20)

    Yesterday and today I came home to find my furnace hadnt been running. I took a look at it (scratching head wondering what everything does) and I noticed the green LED was out. I turned off the power switch and turned it back on again 30 seconds later. Then I heard the pilot light up (electronic ignition) and the furnace run through its cycle. This happened again tonight, but this time it wouldnt start after the above routine. The LED would come on, then the pilot would try to light and then it would all shut down again.

    I went to check my programmable thermostat and everything was still set right. So I went back and ran through my off/on routine and still nothing. Then I noticed that pilot assembly area was filthy so I vacuumed it up a little, but couldnt get too much dust out because my hose was too wide. Then I turned the power back on and held the blower door safety switch and everything started and ran just fine. I think I need to get some smaller brush ends for my shop vac and clean it better.

    Right now the top door is off and everything is running fine.


    I also have taken a look through my owners manual and found a part about the Thermostat Selector Jumper. It says that with a mechanical thermostat it should be at one setting and with an electronic thermostat it should be set a different way. Last year I replaced the thermostat (round one with a dial face) with a programmable. Is that the difference between mechanical and electronic and I shouldve changed that jumper back then? What is the difference in settings?

    Thanks for the help

  • #2
    Re: Furnace and Thermostat questions (Lennox G20)

    The thermostat you put in just last year has failed? Try to buy a Honeywell this time. Stay away from Hunter.

    It's been a few years since I peeked inside a G-20. Are you saying the control board has a jumper for different types of thermostats? I don't remember that.

    The G-20's were famous for flame sensor failures and grounding issues. This may be whats happening to you.

    Comment


    • #3
      Re: Furnace and Thermostat questions (Lennox G20)

      Hows this for an idea? It sounds like he is describing the same symptoms that I have.

      http://www.bobvila.com/wwwboard/messages/52303.html

      Comment


      • #4
        Re: Furnace and Thermostat questions (Lennox G20)

        Yea the Johnson control they put in those was junk. There is a dozen things it could be; the last of which is the thermostat.

        Does the pilot actually light for a few seconds then go out?

        Does the main burner ever come on?

        Does it go into failure mode after 1 try?

        How does the pilot look?

        How soon can Dave Lennox get to your house?

        Comment


        • #5
          Re: Furnace and Thermostat questions (Lennox G20)

          I run into the jumper thing alot. T-stat most likely has a jumper so u can set it up for Electric heat strips....like we use here in Florida OR Gas heat. it is something a lot of people miss.....

          The blinking LED part made me think...dead/low batteries (IF IF IF T-stat has them) again people forget to change the batteries on those with them.

          if the above dont help then Im going with what plumberscrack said and go with Honeywell. (Trun off power to airhandler first...to keep transformer safe if by chance u touch some wires togher).....simple fix for your problem.

          Comment


          • #6
            Re: Furnace and Thermostat questions (Lennox G20)

            Originally posted by plumberscrack View Post
            Yea the Johnson control they put in those was junk. There is a dozen things it could be; the last of which is the thermostat.

            Does the pilot actually light for a few seconds then go out?

            Does the main burner ever come on?

            Does it go into failure mode after 1 try?

            How does the pilot look?

            How soon can Dave Lennox get to your house?
            When I try to restart the unit (shut off main switch at the furnace) the pilot would light for just a few seconds. The pilot would go out and I would try again. If Im lucky, (now that I want to describe exactly what happens it is running fine) the main burner will come on. The green LED will go on when I try to start it and while it is running, but when I turn the thermostat down it will shut back off, I havent gotten any error flashes from it. Do you mean the color of the pilot? It is a good blue.

            Comment


            • #7
              Re: Furnace and Thermostat questions (Lennox G20)

              Soo did u change anything?? or was it just being funky and now working???

              Comment


              • #8
                Re: Furnace and Thermostat questions (Lennox G20)

                Its intermittent. Right now it seems to be working great, but each day when I get home from work it has been out and it is cold in the house.

                I have the program set up like this...

                5:00am to 9:00 70*
                9-4 65*
                4pm to 11 70*
                11pm to 5 am 60*

                This morning my wife said it was cold, I wonder if it stopped working sometime in the 5am to 9 program. Tomorrow I will set it at 70 all day and leave it alone and see what happens

                UPDATE It finally stopped working mid cycle. The furnace shut off and the damper door stayed open. I shut off the power switch and turned it back on again and it started fine.
                Last edited by Orange Apron; 12-12-2007, 07:36 PM.

                Comment


                • #9
                  Re: Furnace and Thermostat questions (Lennox G20)

                  Forget the Tstat. Prolly the flame sensor. Call a local HVAC guy before you end up with no heat

                  Comment


                  • #10
                    Re: Furnace and Thermostat questions (Lennox G20)

                    http://www.lennox.com/pdfs/manuals/L...0%20Manual.pdf

                    "the problem is actually a too low signal thru the pilot assembly. (In which case the I.C. is doing it's job, but the ignition control would have failed eventually. Cleaning the underside of the pilot hood and insuring the pilot orifice is clean helps increase the voltage signal but if you go to all the trouble of removing it, you are better off replacing it, cause it will carbon up in a year or so and you are back to intermittent operation."

                    "Forget the Lennox over priced part. Just replace it with a standard Honeywell universal spark ignition control which is basically all the Lennox replacement is anyway."

                    some quotes from another forum

                    sounds like crack is right again

                    if it were me and i like to save myself some money i would take out the thing and clean the the flame rod real good with some steel wool if you have some or sand paper.

                    from manual
                    Pilot Flame -- Pilot flame must surround the end of
                    flame sensor for proper operation of pilot safety circuit.
                    See figure 7.

                    i always tell everyone with gas in there house to get a carbon monoxide detector (less than 20 bucks at home depot and can save your life)
                    ROMANS 10:9 confess with your mouth that JESUS is LORD and believe in your heart that GOD raised him from the dead and you will be Saved.

                    Comment


                    • #11
                      Re: Furnace and Thermostat questions (Lennox G20)

                      Originally posted by Evil Gopher View Post
                      I run into the jumper thing alot. T-stat most likely has a jumper so u can set it up for Electric heat strips....like we use here in Florida OR Gas heat. it is something a lot of people miss.....

                      The blinking LED part made me think...dead/low batteries (IF IF IF T-stat has them) again people forget to change the batteries on those with them.

                      if the above dont help then Im going with what plumberscrack said and go with Honeywell. (Trun off power to airhandler first...to keep transformer safe if by chance u touch some wires togher).....simple fix for your problem.
                      I cannot tell you how much trouble and money you saved me. I came home from work to find my home at about 85. I couldn't get a hold of my property manager, and knew I would have to suffer until morning. Then I did a search on google regarding problems with thermostats (mine was sort of blinking) and low and behold I saw your comment about the batteries. I never dreamed a thermostat used batteries. Well, I immediately pried off the cover and there were 2 cheap RayOVac AA batteries! I quickly replaced them and the air is now on, AND I AM COOL!! I thanked God and I thank you. You are my hero whomever you are!

                      Comment

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