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  1. #1
    Join Date
    Jan 2020
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    Trane XB80 runs intermittently

    I've got a Trane XB80 that was installed in 2002 when the home was built. In the past week or so it's begun to operate intermittently meaning it doesn't always provide heat when called for. Last night I can see in the data from the thermostat that there was a 2.5 hour period where the thermostat called for heat and the room temperature didn't change which is indicative of the failure.

    When this situation occurs, the code on the main board is 3 flashes indicating "Pressure Switch Error" per the sticker on the inside of the main panel. Sometimes it just starts working and other times a power cycle (completely remove power) of the furnace may get it working.

    When it's not working the behavior is
    1. Inducer motor starts and immediately cuts out
    2. Multiple relay clicks from the main board (I can take a video with sound if helpful)
    3. LED indicates call for heat before switching to 3 blinks

    Here is what I've done so far
    1. Replaced the filter and used a "cheaper" one allowing more airflow
    2. Removed the pressure switch and, with a multi-meter, tested it was switching between open and closed by gently sucking on the input port to supply vacuum
    3. Used a small test tube brush to clean the port on the inducer motor/vent stack
    4. Inspected the connector tube for cracks
    5. Checked the vent stack to be open and clean
    6. Replaced the thermostat with new

    I'm about to condemn the main board but was hoping for some suggestions.

    I read all the FAQs and see a lot of no DIY posts yet the registration says Homeowners welcome.

    I'm looking for further steps on isolating the problem and nothing about advice on how to do the actual repair or replacement. I like know what needs to be done before I call an HVAC company.
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  2. #2
    Join Date
    May 2004
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  3. #3
    Join Date
    Aug 2002
    Southold, NY
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    You can condem and replace several parts or get someone with tools and knowledge to find out what’s exactly wrong.

  4. #4
    Join Date
    Sep 2008
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    How did you post pics on your first post? That's what's interesting to me...
    "The only true wisdom is in knowing you know nothing" Socrates

  5. #5
    Join Date
    Aug 2009
    Beatrice, NE
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    Pressure switch errors come in 2 types, not closing when they should close, not opening when they should open. Your test by sucking on the tube really did nothing to prove good or bad as there is a pressure that it should open and another it should close at. You know it opens and closes but not the pressure it is doing it at.

    You need a tech to come in and evaluate the furnace, see if it is doing what it should. As I see it you have an intermittent problem. Don't be surprised when the tech tells you it worked fine while they were there. They should check the pressures I referenced earlier and know if they are in or out of spec which may be a clue. Without the pressure est they are just guessing.

  6. #6
    Join Date
    Sep 2007
    edmonds wa
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    At that age get a good tech on it.
    UA Local 32 retired as of Jan 2020

  7. #7
    Join Date
    Aug 2008
    Hibbing, MN
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    It could be a bunch of different things. As posted, get a good tech to hook up a manometer, check your pressure switches, and your inducer motor. He/she will also evaluate your venting, heat exchanger, etc. You’ve done as much as you can. I wouldn’t replace the board unless you have money to throw away.
    If God didn't want us to eat animals... He wouldn't have made them out of MEAT.

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