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  1. #1

    High Limit Still Tripping

    Goodman GMP100-5 RevB
    990260247
    Horizontal, supply terminating on left side.
    I checked everything I can think of to check. No obstructions blocking airflow. I even pulled off plenums and still tripping. Limit is good. Temp gets to 240 in about 5 minutes.Gas pressure was at 3"wc so I can't turn it up cause it will trip quicker. No obstructions in flue. I pulled that off too and still tripping. I ran combustion test and nothing out of ordinary. It still runs at 81% efficiency before it trips. I pulled blower out and everything was clear. I could see all the way through. Blower cap and motor okay. I calculated cfm at 1851 cfm with a 40 degree heat rise. I tried to run in all different speeds and still tripped.The unit is only getting super hot where the limit is. Normal temps at top and bottom of heat exchangers. Never ran into this problem..suggestions are kindly welcomed cause I'm pulling my hair out on this one.
    Ray in Texas

  2. #2
    Join Date
    Feb 2005
    Posts
    284
    could be holes in heat exchanger or insulation covering limit so it dosent get airflow on it

  3. #3
    Looked at it. It looked great with no signs of outer wear and no rust. Combustion heat exchanger test was good. no levels of co in supply air. A friend told me about rings coming loose. I am inclined to believe this is the case.

  4. #4
    Join Date
    Feb 2005
    Posts
    284
    exactally,i forgot about those rings

  5. #5
    What kind of filter are they using? Had similar problem and it was one of those damn filtrete extra allergen filters its like sucking air through a paper bag. If everything else is good its got to be airflow.

  6. #6
    They were using cheap rock catchers..took filter out and left door open. I also cut big hole to add more return in plenum. Temperature still rose..I also took the top of the transition plenum off of supply plenum and ran with blower door open and unit still tripped with temperature rising the same..

  7. #7
    When I get a limit tripping I'll pull one of the screws out right at the limit and take the reading right next to it.

  8. #8
    Quote Originally Posted by davej89 View Post
    When I get a limit tripping I'll pull one of the screws out right at the limit and take the reading right next to it.
    I did that with wire thermometer. It is tripping where it is supposed to at around 240f.

  9. #9
    Man you tried everything. Im stumped got to be the heat exchanger. I'd get my snake camera and check it out or we use a dye test on the outside of the heat exchanger to look for cracks.

  10. #10
    Join Date
    Jul 2009
    Location
    S.E.,PA
    Posts
    99
    I would try setting gas pressure at 3.5 unless marked otherwise. Verify that the unit has the correct sized burner spuds and that they haven't been reamed out by someone else. Check the venter motor and wheel to make sure the motor is ok and that the wheel isn't missing any fins, birds stuck below the wheel, gasket condition. Sounds like you got a good one. Also check the burners/ venturie holes for rust, obstructions.
    Even a blind squirrel can find a nut every now and then.

  11. #11
    Join Date
    Jan 2011
    Location
    Ottawa, Canada
    Posts
    388
    What about the limit being posiitioned too close to the HX? ie: bend and touching? Do you have another limit to try in its place?

  12. #12
    Join Date
    Jan 2011
    Location
    Ottawa, Canada
    Posts
    388
    What about a mis-aligned burner? Heating up the HX port too much at the limit location?

  13. #13
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    oversized ?

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