PG9M Intermittently working error 31

Discussion in 'HVAC Heating & Cooling' started by mcameron68, Dec 30, 2018.

  1. mcameron68

    mcameron68 New Member

    Joined:
    Dec 29, 2005
    Location:
    California
    Hey guys, been trying to figure out my issue here on my attic mounted PG9M furnace.

    I have been getting error code 31, but only when it doesn't work. Seems like every time I go up there it does work so I have only seen the code one time. The one time I saw it, the inducer did run, but the heater never fired and I got that error code.

    I cleaned the flame sensor (not related to that code, but it was recommended) and I also cleaned out the trap which was not dirty.

    I do not have a manometer, but I suspect its the pressure switch itself since it works normally much of the time.

    This morning the low was 37 degrees and the heater would not fire at all. After watching a couple shows and getting up in the attic to see if it was the same code, it fired right up with no errors. By this time it had warmed up 15 degrees outside. This makes me believe that there is not any kind of restriction anywhere causing the problem. It does seem like the warmer it is, the more likely it will run fine, so I am wondering if the switch is impacted by the cooler weather.

    Furnace was installed in 2011, so its relatively new.

    Am I totally off base?
     
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