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US Boiler K2FT-110 making loud humming noise

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Joe_5
Joe_5 Member Posts: 19
in Radiant Heating
Installed this direct vent condensing boiler last year for a friend and it ran perfectly and super quiet all last winter. Job is all radiant in slab. A few weeks ago he started hearing a loud humming noise when running with an occasional ignition lock out. Humming noise starts as soon as burner ignites and I can quiet it by slightly restricting inlet pipe with my hand until it smooths out. Gas inlet pressure OK, used combustion analyzer and adjusted both high and low fire per manual but noise is still happening. I feel like when I talk to rep on Monday they will tell exactly what is wrong but I can't wait. Any ideas??? Joe

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  • Ironman
    Ironman Member Posts: 7,376
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    Is there any CSST in the gas line?

    Your fuel to air mixture is probably too lean. Adjust it to the richest mixture that the I/O manual allows.

    Both of these can cause frog-horning and the latter can cause ignition failure.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Joe_5
    Joe_5 Member Posts: 19
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    Ironman, No csst, noise is not from piping. We could be on the leaner side of what the manual allows but no matter what we did it didn't change the possibility of that noise. The boiler starts at a high fire rate and then modulates to the need at the time. We increased the minimum rate and decreased the max to try and keep it at a good firing rate for now to avoid the noise but it didn't always prevent the "frog horning" which seems like a good description. I can't get back to the job until monday anyway. On another note it seems that all of the videos on US Boiler's website site reference a totally different design of heat exchanger, I wonder if the old design was a problem....
  • Joe_5
    Joe_5 Member Posts: 19
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    Holidays got in the way of responding but I do have a resolution for my problem. I spoke again with US Boiler and they sent me a document that detailed a few fixes which made this boiler run like it did when new. The noise was 99% removed by drilling a hole in the intake attenuator. We hear a hum in the very beginning but then it clears itself. They also had me cut a wire that was tied into the flame sensor wire. This wire was located low in the boiler and I believe it was an attempt to sense if the condensate drain was blocked. After these mods we redid the combustion testing and we were able to get it to light and stay lit even at low fire. This was almost two weeks ago and the problems haven't returned. Fingers are crossed...
    IronmanDZoro

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