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    Flame inside burner tube (9 Posts)

  • Pendis Pendis @ 6:09 PM
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    Flame inside burner tube

    I have a Weil Mclain HE II boiler. Propane gas. Installed new in 1996.  All original with the exception of the control module (replaced about 2 years ago and the blower motor (replaced about 4 years ago).  Over the last year I have noticed an intermittent problem with flames in one or more of the burner tubes(there are 10 in this boiler). Generally it happens in the 2nd tube on the right side of the manifold closest to the gas valve. Occasionally it happens in some of the others, but always on the right side of the manifold.  The tubes are clean and in very good condition as well as the orefices.  Could this be a pressure problem? If so, how can I measure the pressure and adjust if necessary? Any helpful feedback would be greatly appreciated.
  • Tim McElwain Tim McElwain @ 6:31 PM
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    This is known as

    "Flashback". It is usually the result of an out of adjustment gas and air mixture causing the flame velocity to exceed the flow velocity. Typically a slight adjustment to the air shutter will take care of it.Closing the air shutter a very small amount. This should be done by a professional who should also do a combustion test on your equipment along with cleaning and adjusting any thing else that may need attention. The flame on a properly adjusted gas burner (natural or propane) should be a soft blue flame, not roaring or lifting.

    Was this happening during very cold weather? If so it could be the result of poor vaporization of the liquid from the tank into the piping system. See if it goes away with a temperature increase.
  • Pendis Pendis @ 8:35 PM
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    Flame inside burner tube

    Hi Tim, Thanks for the response. The flames across all 10 tubes is normally soft blue with no jumping.  The only time it isn't is when there's "Flashback" and only confined to those tubes.  The weather doesn't seem to have any effect.  It just happens intermittently.  Correct me if I'm wrong but I don't think this unit has air shutter adjustments.  Wouldn't the air flow be regulated by the blower motor? If thats the case would the problem likely be the gas pressure?   
  • Tim McElwain Tim McElwain @ 7:21 PM
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    I need to dig

    out my manual on the HEII to get an idea on its sequence. I will get back to you.
  • Empire Empire @ 5:24 PM
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    Burner....?

    Not sure of what you have since the manual is not in front of me.  If your burners are short, say 5 6" they are "in shot" burners which do not have air adjustment on them.  Ribbon burners will be substantially longer and sometimes do have air adjustment.  Gas pressure for boiler must be checked and Combustion analysis must be done.  This can rule out an often times ignored or missed restrictor plat on the inlet to IDM induced draft motor.  The only reason I say that is that you said it was replaced.  The only way to check the orifices is to remove and visually checked for debris or spider nests...etc... 

    Mike T.

    PS; Time will set you straight.
  • Pendis Pendis @ 2:56 PM
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    Flame in burner tube

    Hi Mike, I have removed all the orifices from the manifold, vaccumed out the manifold and each orifice.  All is clean and unobstructed.  Theses are longer tubes and have no air adjustments. Maybe a combustion analysis and gas pressure test is the net step.  Thank you for the input.
  • Empire Empire @ 5:27 PM
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    Burner....?

    Not sure of what you have since the manual is not in front of me.  If your burners are short, say 5 6" they are "in shot" burners which do not have air adjustment on them.  Ribbon burners will be substantially longer and sometimes do have air adjustment.  Gas pressure for boiler must be checked and Combustion analysis must be done.  This can rule out an often times ignored or missed restrictor plat on the inlet to IDM induced draft motor.  The only reason I say that is that you said it was replaced.  The only way to check the orifices is to remove and visually checked for debris or spider nests...etc... 

    Mike T.

    PS; Time will set you straight.
  • Bob Harper Bob Harper @ 9:22 AM
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    flashback

    As Timmie said, flashback is a function of too much primary air, too low manifold pressure or I would add high port loading or mechanical defects impeding the natural flow of mixed gas to the burner ports. Often, a subtle mis-alignment in the burners or how they are engaged with the burner orifice spud can do it. Gauge the burner orifice to ensure it is spec. Sometimes on LP, this can happen with the burner tilted uphill. Perform combustion analysis and look into each burner while firing. Try switching burner tubes to see if it is the tube or the position. Make sure there are no vent restrictions in the HX or common vent and you have proper draft--too high or too low are problems.  Lastly, when in doubt, measure the manifold pressure directly off the valve downstream before the burner where possible. You need to ascertain if this is due to an increase in flame speed vs. a mechanical defect.

    HTH
    This post was edited by an admin on February 8, 2013 9:23 AM.
  • Pendis Pendis @ 3:22 PM
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    flashback

    Hello Bob, One orifice a few years ago was misaligned because the threads were stripped as it was screwed into the manifold (during the original install). This was definitely causing flashback in that particular tube.  I replaced the orifice, threaded it correctly and the flashback dissapeared.  All of the orifices are threaded correctly and I don't believe any are misaligned.  When you talk about the burner being tilted uphill are you referring to a misaligned orifice?, or the burner tube tilted up because it is not seated fully into its slot?  This problem is very strange because most of the time evrerything works perfectly and every so often 1 or 2 of the tubes have flashback.  Generally its the same 2 tubes on the right side of the manifold. In the meantime, I'll look for any air flow restrictions and switch the 2 tubes to the opposite end of the manifold.  Appreciate your help.
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