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  1. #1

    RTU burner cutting in and out

    Unit: Lennox GCS16-411-100-1P Packaged rooftop

    So the burner on this rooftop unit keeps cutting in and out when it first starts. I inspected the heat exchanger for any holes but didn't see any; although the style of heat exchanger makes it difficult to fully inspect.

    As soon as the flame drops out the ignitor fires again and the burner lights so the flame sensor is working correctly. Voltage is continuous to the gas valve through all of this so its not the ignition module.

    I put my manometer on the outlet of the gas valve but naturally I couldn't reproduce the problem at that point. The customer says the unit will run for a while and then lockout and then eventually come back on.

    Im wondering if the flame is getting blown out by something (the building is on the shore of Lake Ontario and its been very bad weather lately) or if the gas valve is having trouble staying open despite proper voltage.

    Hazard a guess.

    Heres a link to a video of the problem. http://s38.beta.photobucket.com/user...e26ae.mp4.html

  2. #2
    Join Date
    Nov 2006
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    Southeastern Pa
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    18,385
    I think this one is more for the pro technical forum.

  3. #3
    Join Date
    Nov 2004
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    up in the hizzy
    Posts
    1,376
    nice rifle

  4. #4
    Join Date
    Nov 2012
    Location
    Macomb Twp MI
    Posts
    50
    Nice video, or random pics of you and chicks, whichever.

  5. #5
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    4,590
    Is that a Catilina or Bonneville?

    Might want to change your photobucket settings to "private"
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  6. #6
    Join Date
    Feb 2012
    Location
    Durham, NC
    Posts
    73
    One sick photobucket account

  7. #7
    Join Date
    Feb 2012
    Location
    Tyler, Tx
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    11
    Gonna have to check gas pressure. If that checks out pull it apart to check exchanger.

  8. #8
    Join Date
    May 2000
    Location
    Salem, WI US
    Posts
    61
    Check flame signal and gas pressures. I have had momentary voltage drops at the wiring connection on limits cause this scenario as well.

    Beta

  9. #9
    Quote Originally Posted by 2sac View Post
    Is that a Catilina or Bonneville?

    Might want to change your photobucket settings to "private"
    Its a Grandville actually. Same thing though. I haven't used that photobucket account in ages hence all the BS in there.

    Every time I connect a manometer I cant reproduce the problem. It appears if the flame is going out, then the flame sensor is seeing it and restarting the ignitor and not the other way around which means the flame is going out from an outside source, so to speak, rather than being shut off from flame failure.

    I guess i'll have to start changing some parts if i can't get the gas pressure to check out.

  10. #10
    Join Date
    Jun 2004
    Location
    Eugene, Oregon
    Posts
    1,018
    You said you checked the voltage to the gas valve while this is happening. Did the voltage fluctuate when this was happening? I'm wondering if the gas valve coil is bad and dropping in and out. If so, you should see a voltage fluctuation. If the gas valve is good I would suspect something is disrupting the flame. HX, inducer, wind sheer.....etc. You said the weather has been bad. Perhaps something temperature related.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
    "Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain
    http://www.campbellmechanical.com

  11. #11
    Quote Originally Posted by air1 View Post
    You said you checked the voltage to the gas valve while this is happening. Did the voltage fluctuate when this was happening? I'm wondering if the gas valve coil is bad and dropping in and out. If so, you should see a voltage fluctuation. If the gas valve is good I would suspect something is disrupting the flame. HX, inducer, wind sheer.....etc. You said the weather has been bad. Perhaps something temperature related.
    I didn't really see voltage fluctuation but it happens so quick and my meter doesn't respond instantly, especially in -25C. There is no pilot on this so it just opens the valve and starts the ignitor when it sees flame failure and its only a fraction of a second between dropout and reignition so its really hard to figure out where its coming from. I think i'll just see about switching the gas valve out with something I have laying around to eliminate that possibility.

  12. #12
    Join Date
    Jun 2004
    Location
    Eugene, Oregon
    Posts
    1,018
    Quote Originally Posted by TheDecline View Post
    I didn't really see voltage fluctuation but it happens so quick and my meter doesn't respond instantly, especially in -25C. There is no pilot on this so it just opens the valve and starts the ignitor when it sees flame failure and its only a fraction of a second between dropout and reignition so its really hard to figure out where its coming from. I think i'll just see about switching the gas valve out with something I have laying around to eliminate that possibility.
    Try tapping on the valve to see if you can duplicate the problem.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
    "Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain
    http://www.campbellmechanical.com

  13. #13
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,385
    Wow. I had forgotten about the Grandville.

    Are you seeing any variance in the flame rectification current prior to the unit trying to restart?

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