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Backflow vent started leaking

jlonjjlonj Member Posts: 22
Just turned on my boiler a couple of times this season, and it's been acting a little bit odd. I am trying to get it looked at by a pro on here, but just wanted to check with this board. The boiler itself is pretty new... replaced in 2015.

First, the backflow vent has started dripping. Second, the radiators used to traditionally whistle as the steam came on. That whistling is gone. I also have a sense that the system is filling with steam slower than previous years. Anyone had these symptoms or have an idea of the cause?

I had mentioned in a previous post that I think my manual fill valve has a leak because the boiler water level was gradually growing. I was planning on having it replaced when I had the boiler cleaned this season. I'm wondering if as my boiler builds up steam, it is pushing the incoming water drip into the backflow? I'm not a steam expert, but it's just the only thing I can think of... Or is that not related?


  • Jamie HallJamie Hall Member Posts: 12,696
    Probably not related. The drip from the backflow preventer's vent indicates -- and is supposed to indicate -- that at least one of the valves inside isn't seating properly, and it can't do it's job correctly. Sometimes it's just bit of grundge. Sometimes not. Most of them can be repaired.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • jlonjjlonj Member Posts: 22
    @Jamie Hall thank you! One question I do have is that I noticed a lot of water around the boiler. I’ve come to find out the backflow vent is continuing to drip even after the boiler has been off for >12 hours. Is this normal for a malfunctioning backflow preventer? I’m not sure where it’s getting the water... the boiler level isn’t going down.
  • mattmia2mattmia2 Member Posts: 1,173
    It is city water from the water supply. as mentioned above it is designed to leak water out the relief if the backflow mechanism malfunctions, you need to repair the backflow valve
  • jlonjjlonj Member Posts: 22
    edited October 2019
    @mattmia2 But I have a manual water feeder valve between the supply and the backflow preventer that is in an off position. How is the city water getting past that? Does that confirm the manual feeder valve is failing? Sorry if these are stupid questions!
  • mattmia2mattmia2 Member Posts: 1,173
    Most likely the manual valve isn't holding. The experts would know better but the very low pressure trickle from the valve might be why it is leaking out the relief.
  • HomerJSmithHomerJSmith Member Posts: 878
    There's no such thing as a stupid question. As my mentor said, "A stupid question is better than a stupid mistake."
    STEAM DOCTORmattmia2
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