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  1. #1
    Join Date
    Oct 2004
    Posts
    14
    Can anyone give me an idea of what is causing the furnace to cycle the gas feed to the burners on for 10 seconds, then off for 10 seconds for the duration of time the thermostat calls for heat?

    Thanks.

    Jim.

  2. #2
    Join Date
    Nov 2001
    Posts
    1,874
    It could be the stat, or the flame sensor, or dirty filter.
    Although I wouldn't think a limit switch would cycle that fast.
    What kind of t-stat do you have ?
    Is it round and gold, with needles to indicate the temps.
    Or is it a digital read out ?

    Normally if it's not detecting a flame and goes off due to that, the unit will lock out after 3 or 4 trys to light.
    So it could be doing what the stat is telling it to do.
    Short cycling.


    If you try to fail, and succeed.
    Which have you done ?



  3. #3
    Join Date
    Oct 2004
    Posts
    14

    Not the stat.

    Toolpusher...

    Thanks for the reply...

    The stat calls for heat and releases just fine over a long period of time. All of the on and off is occurring during the duration of time the stat calls for heat. In other words, the stat is not cycling every 10 or 20 seconds like the burners are. Also..because I wanted a new stat, I have had 3 different ones working the unit. The burners exhibet the same 10 seconds on, 10 seconds off with all stats.

    Jim.

  4. #4
    Join Date
    Feb 2004
    Posts
    2,458
    I would agree the flame rod first place to start. Clean flame rod.

  5. #5
    Join Date
    Jan 2005
    Location
    Ontario
    Posts
    164
    Is it a new furnace?? If it is, check to see if it's grounded properly.
    Also any codes from the L.E.D's?? and check to see if your getting a constant 24v on the "w" terminal.

  6. #6
    Join Date
    Apr 2003
    Location
    Iowa
    Posts
    763
    clean the flame rod.....make sure the wire is intact all the way to the board.

  7. #7
    Join Date
    Jul 2003
    Location
    Rochester NY
    Posts
    160
    Some models had upgrade flame sensor kits.
    Lennox-parts.com

  8. #8
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,584
    Let the Lennox unit go through this for (3) cycles and then check the fault code (light blinking)and that code is usally on the door.
    I would also check flue,draft motor as Lennox has had some problems with draft motors.80MGF models.

    The flame sensor can be cleaned by turning off power to unit, then left side of furnace (1) burner you will see a ceramic type steel rod with (1) wire connected to it. Remove wire, remove screw holding sensor, clean with steel wool, re-install and re-connect wire.
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  9. #9
    Join Date
    Jan 2005
    Location
    Ontario
    Posts
    164
    Yeah, 80mgf's and g24's had flame sensor problems, but that was around '95. Also some of the early mid's had a painted ventor motor, and the paint would flake off from the heat and screw up the pressure switch.

  10. #10
    If this is a newwsystem or you recently had electric work done check polarity to furnace

  11. #11
    Join Date
    Jan 2005
    Location
    yadkinville nc
    Posts
    528
    Can you give me the model number please and what kind of thermostat is it would not happen to be a Honeywell digital 4 wire hook would it?

  12. #12
    Join Date
    Oct 2004
    Posts
    14
    I will have model and serial number tomorrow. Current stat is a new honeywell 8500 digital with 4 wire hook up. However...furnace had the same problem with a Rite-Temp 4 wire digital too.

  13. #13
    sounds like polarity to furnce is wrong

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