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Goodman GMPN gas furnace shuts down

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patrickor
patrickor Member Posts: 2
in Gas Heating

Hello,

I'm new to this forum.

My GMPN shuts down after about 2 to 3 minutes. Pressure switch closes when inductor fan runs. Flame sensor cleaned, then replaced. It measures proper micro Amp reading (~4 uA) when flame is present. Control board replaced (twice); no flash codes from status LED. No roll-out interruption.

What am I missing? Any help appreciated.

Patrick

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,891

    So I take it that the inducer starts, pressure switch proves air, pilot ignites are you getting main flame at all? I see this furnace is hot surface ignition is it glowing?

    You could try jumping the pressure switch after it proves (Temp…don't leave it this way) it could be momentarily opening when the main gas comes on.

    You will have to check for 24 volts at the gas valve. Is it powering the gas valve at all?

    I see it has stack over temp switch, roll out, high limit etc.

    patrickor
  • Ironman
    Ironman Member Posts: 7,886

    If the condensate drain or trap is partially clogged, that can cause what you’re describing.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    patrickor
  • HVACNUT
    HVACNUT Member Posts: 7,307

    Trial for ignition takes less than 2 to 3 minutes, so flame is established across all burners, runs for a minute or two, then the flame drops out? Does the blower come on during this process? Does it keep repeating the process but never locks out?

    If you have a meter that can capture readings, test all safeties and limits one at a time and see what opens first in the series.

    patrickor
  • patrickor
    patrickor Member Posts: 2

    I finally got back to this…and none too soon as the outdoor temp is falling.

    I'm actually not sure what was happening before but I'm now at a point where the furnace will only run if I reset the top roll-out switch. Then it will run for a few minutes, until the roll-out switch opens, and flame goes out. I realize this is normal operation for safety.

    I'm not sure what the flame should look like. I've seen a few extreme examples of roll-out on youtube but mine looks nothing like those. However, the flame from one burner (middle one of three) does appear less defined and does seem to lick back a bit into the burner box. It seems the most likely reason for this is a cracked heat exchanger. Needless to say, I hope that is not the case. I tried a new roll-out switch: same thing.

    I did connect a manometer to the vacuum port on the inducer fan while running the circulation fan and observed no reading. Wishful thinking? Any other possible cause(s) for tripped roll-out?

    Thanks to all.

  • pecmsg
    pecmsg Member Posts: 6,893

    time to call for service!

  • Ironman
    Ironman Member Posts: 7,886

    Cracked heat exchanger. Not surprising considering the age of that furnace.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • pecmsg
    pecmsg Member Posts: 6,893

    I’m not ready to condemn it but it’s pointing that way.

  • SuperTech
    SuperTech Member Posts: 2,646
    https://forum.heatinghelp.com/discussion/comment/1875348#Comment_1875348

    Blocked vent maybe? Any horizontal sections of the vent pipe back pitched? Is the secondary heat exchanger plugged?

    A combustion analysis with a digital combustion analyzer would be really helpful for figuring this out, it would eliminate a lot of guess work.

  • HVACNUT
    HVACNUT Member Posts: 7,307

    Check draft with the blower motor off, then blower motor on, without the heat. Fan only. Check venting and combustion air. Check gas pressure. You say you don't notice anything, but temperature is obviously building up in the burner compartment. Do you notice any change in flame pattern when the blower motor comes on?

  • gpjazz
    gpjazz Member Posts: 40

    Simple… It's got a bad heat exchanger. That's it.

    Some of those had lifetime warranty. Some had 20 years I think. Call distributor and find out if it's still in warranty or not. If it is, then it's very easy to replace heat exchanger. Should take less than 2 hours.

    If not in warranty, then time for new furnace.

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