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Munchkin wet controls

I am working on a M# 199, 2004 vintage boiler. It is a modular system with 2 matched boilers. The customer complains that it backfires every couple of days. 2 months ago we had replaced the burner, gasket, door, insulation, electrode and flame rod. Yesterday, when I took the cover off, it seemed damp. On the top edge of the base there was moisture from the gas pipe to the control board. I couldn't find the leak, all the sensors, pipe and manifold connections and insulation were dry. I finally found it moist air coming from from the air venturi opening. There is no sign of a leak inside and there is no condensate (I have checked the trap and it is clean) during the off cycle.

Has anyone run across this before?

I am thinking i must have a small leak that evaporates all the evidence due to the hot heat exchanger.




  • icesailoricesailor Member Posts: 7,265
    Wet Minchkins:

    When you cleaned it, did you notice if there was a high tide line inside the burner chamber? Did you take an old credit card and run it between the sections and get them all clean"

    And are you sure that the drain is totally clear? I had one recently that seemed to be draining fine but was actually quite restricted. On a cold start-up and a long run, the condensate would overwhelm the drain and fill the chamber.

    Stick your combustion analyzer inside the outside vent. See what kind of CO you are getting.

    You can also frill and tap a 1/8" brass plug in the outlet because they are almost always Sch 40 PVC.
  • Steve WhitbeckSteve Whitbeck Member Posts: 669
    edited February 2012

    What you have is after the burner shuts off the blower runs to clear the hot moist fumes from the combustion chamber. Those fumes rise out of the intake horn into the inside of the boiler. The newer boilers run the blower longer to stop this problem. When I service the older model boilers I record their settings and then reprogram the 925 controller to the newer program to make the blower run longer - this helps..  What do your vent terminations look like? Do You have at least 18 inches vertical seperation between the intake and the exhaust pipes?
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