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  1. #1
    Join Date
    Dec 2010
    Location
    Goodyear, AZ
    Posts
    56

    Condensing furnace not firing off

    Need some help on this one guys.
    Brand new Trane/Am.Standard TDC120 condensing furnace not firing.
    It ran through the sequence; inducer-HSI-gas valve opens-no flame-shut down.
    I've got 24 v coming from the board. Gas valve works. Bled the gas line.
    I removed the cover to the combustion chamber and the sucker fired off. Ok blocked flue pipe right?
    I removed all of the flue piping, both the intake and exhaust. Took all the external flue piping out of the equation. Put the cover to the chamber back on and the problem returned- no flame.
    When it does fire (with chamber cover off) the flame looks good, nice blue tight flame, not dancing at all.
    Any ideas?
    Thanks brothers

  2. #2
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,348
    Gas pressure?

  3. #3
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,855
    How are the flues ran? What size?

    Has the igniter moved? Try repositioning it

    To me, it sounds like with the cover on, your pressure switch is not making.


    Sent from my iPhone using Tapatalk

  4. #4
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,855
    Maybe the plates under the intake screen has shifted


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  5. #5
    Join Date
    Dec 2010
    Location
    Goodyear, AZ
    Posts
    56
    Sequence gets hung up after gas valve opens-no flame-lock out.

    If it was draft pressure switch, it would lock out earlier in the sequence.

    With the pressure switch open, it wouldn't proceed to light the HSI.

    It's weird. Even with the chamber cover in place and the flexible intake tube removed, so there's just the 3" opening to the chamber, it never fires off. The cover has to be removed to for it to fire up.

    I was starting to think, cracked heat exchanger, plastic shavings from the PVC pipe getting sucked into the burners, I'm stumped

  6. #6
    Join Date
    Jul 2013
    Location
    Harrisburg, PA
    Posts
    288
    Somehow your air intake must be blocked if it fires without the cover on. You have fuel and the igniter works; the only thing left that's needed for combustion is air.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,929
    Check manifold pressure. Is HSI loose.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Feb 2008
    Location
    Altmar, New York, United States
    Posts
    4,618
    lp or nat?

  9. #9
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,348
    Quote Originally Posted by CoolShowers View Post
    Somehow your air intake must be blocked if it fires without the cover on. You have fuel and the igniter works; the only thing left that's needed for combustion is air.
    But how much fuel is being delivered? Need gas pressure.

  10. #10
    Join Date
    Dec 2013
    Location
    toronto ontario
    Posts
    3
    what outdoor tempature do you have if the venting size is marginal in cold weather you won't pull enough air through the intake double check your gas pressure lock it to high fire

  11. #11
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,348
    Ho. Lee. Crap. Is it really only 33* just outside of Phoenix!!!???

  12. #12
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    2,068
    There is a 1/4" tube that the gas valve uses to reference burner box pressure. I am not sure how it would affect the gas valve but I have a suspension that there is a connection there. When you set the gas pressure you either have to reference the burner box or take the cover off on the old units, newer units don't have the option you have to "T" into that line to set the gas pressure correctly.

  13. #13
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,855
    So...with the cover on it doesn't fire. With the cover off it does.

    What is blocking the inlet on the inside?


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