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Dunkirk Q90-100 II Boiler Fails to Start (S/N341200046)

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dksagun
dksagun Member Posts: 6
edited January 11 in Gas Heating
Boiler fails to start with the pressure switch tubing attached to the intake vent pipe fitting. Please see attached picture markup for location. Boiler starts and runs okay with tubing disconnected from the fitting on the intake vent pipe line. Verified intake vent pipe is clear and free from obstruction.. Both pressure switches have been replaced without resolution. Please advise as to what the resolution to this problem could be.











Comments

  • Ironman
    Ironman Member Posts: 7,376
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    Check the condensate drain and trap for blockage.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Big Ed_4
  • dksagun
    dksagun Member Posts: 6
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    Condensate trap has been replaced. Only fails to start when pressure switch tubing is connected to vent pipe. Bent pipe is free of obstructions 
  • Ironman
    Ironman Member Posts: 7,376
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    The only way to confirm that a pressure switch is accurate is with a manometer.

    Are you sure that you have the correct switches and they’re properly connected?

    If the original switch was tripping, the cause for it should have been determined rather than replacing it. You don’t replace a safety for doing its job.

    The only way to properly diagnose this is with a manometer to confirm what’s going on. Assuming that the switches are functioning correctly, then there has to be a restriction somewhere or the combustion blower is not performing properly.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    GGross
  • dksagun
    dksagun Member Posts: 6
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    The pressure switches are installed in the correct position. I verified there are no restrictions in the lines. The combustion blower inducer motor was replaced in January 2023 for another issue, but it did not resolve the problem. Based on all that has been replaced what could be the cause of the problem? This issue has been ongoing for a few years. I just leave tubing disconnected, but am looking to get it resolved.
  • 109A_5
    109A_5 Member Posts: 1,386
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    Hello @dksagun,
    Sadly these I/O manuals as with others is on the lame side regarding a situation like yours. Also it does not seem to accurately cover your version with the two pressure switches.

    This page, scroll down and click on Archived Documents button, has many manual versions of your unit. Not sure which best fits your unit.
    https://dunkirk.com/product/condensing-gas-boiler-q90/

    This one, although the at beginning is for conversion instructions, acknowledges the additional pressure switch and may have information that will help you.
    https://dunkirk.com/wp-content/uploads/2022/03/90-Series-Conversion-Kit-Instructions-DSI-to-HSI.pdf

    You may have to buy or build and use a Manometer to better understand the situation. Seems odd that it will run with the hose disconnected.


    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • dksagun
    dksagun Member Posts: 6
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    I do have access to a manometer. Never used one though. I will look over the documentation and give it a try. Wondering if there may be an issue with the IBC unit not monitoring the pressures correctly?

  • 109A_5
    109A_5 Member Posts: 1,386
    edited January 13
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    Hello @dksagun,
    Depending on how sophisticated the control board logic is I suspect the controller is looking for a COS (Change Of State) between the Violet wires (open to closed or closed to open) at a certain point in the startup sequence, to prove draft. Once running another COS may shut it down (lack of draft). If in the wrong state at a call for heat it won't continue with the startup sequence.

    Any error codes ?




    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • dksagun
    dksagun Member Posts: 6
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    No error codes available with this IBC. Just has LED’s to indicate what state the boiler is in. Igniter and Valve LED’s comes on then shuts down as the Flame LED starts to come on.  The differential and negative pressure switches have been replaced without resolution. 
  • 109A_5
    109A_5 Member Posts: 1,386
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    Hello @dksagun,


    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System

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