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Steam Pipe Heating - Knocking

AGPR21 Member Posts: 7
edited December 2021 in Strictly Steam
Hello. We have a one - pipe steam heating system (located in Chicago) that is experiencing water hammer or knocking in what appears to be one particular area where a repair clamp was placed.  It is also near where what appears to be a trap is located as well.  We are contemplating replacing the section of pipe where the clamp is hoping the new section will prevent water from being trapped there.  Or do the traps need to be replaced on this area?  Which is a return line headed back to boiler.   NEED HELP!


  • Can you post some pictures of the pipe and trap in question?
    Generally a one pipe system will not have traps like a two pipe system.—NBC
  • AGPR21
    AGPR21 Member Posts: 7
    Thanks for responding.  Sure.  See pics below of the return pipe in the one pipe system. 
  • AGPR21
    AGPR21 Member Posts: 7

  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    That's not a trap, it's just a capped pipe (if I'm looking at what you are calling a trap). it might be where the return used to go under the slab, or it might have been used for flushing the wet return.

    The horizontal portion that is above the floor...how high is it compared to the water line on the sight glass? As long as it's well below there shouldn't be any hammering coming from there.

    If it's right at the boiler water line, that could be the cause.

    I will say it can be difficult to find the actual place where the hammer is happening...the sound travels around the pipes

    Maybe some more pictures of the rest of the system will help us see something.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • KC_Jones
    KC_Jones Member Posts: 5,737
    That's a wet return pipe. Banging is from steam and water existing, unhappily, in the same space. That pipe should never get steam in it.

    How does the height of that pipe relate to the water line of the boiler?
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • AGPR21
    AGPR21 Member Posts: 7
    Here are a few more pics including measurements.  Didn’t think of the fact that steam would not be present in that pipe.  Also sucks that where the noise sounds does not mean where it is originating from.   Gotcha.
  • AGPR21
    AGPR21 Member Posts: 7

  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    Nice work with the tape measure--so that horizontal pipe (the wet return) looks to be well below the waterline, so to me that would rule out that area as a source of hammering.

    Look for areas of the main piping (the higher horizontal pipe that has the radiator runouts coming out the top of it) where it is sagging and could trap any condensation from getting to a vertical drip pipe that goes down to the wet return.

    Also, how is the water level of this boiler during a firing cycle? Is it pretty steady or does it drop dramatically at times (like greater than 2")
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • AGPR21
    AGPR21 Member Posts: 7
    Thanks for your response!  Gotcha. I will inspect the main piping for sag areas.  I’ve read gurgling near vents is bad as well?  Also the two radiators right above the suspected section seemed to have a little water in them.  I emptied both.   But the knocking was in the wet/dry return. As far as the water level it seems to drop to about 1/4 of the full tube.  Maybe lower during the firing cycle.  Lastly the main piping is un insulated.   Not sure if that contributes or not. 
  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    The main piping being uninsulated may not be all of the problem -- probably not -- but it surely isn't helping.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • delcrossv
    delcrossv Member Posts: 742
    Little off topic, but what's with the double regulators? Lo/hi burner?

    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
  • AGPR21
    AGPR21 Member Posts: 7
    Yes.  For a hi lo mode.  
    JUGHNE Member Posts: 11,060
    Can you elaborate on how that hi-low works?
    The gas must flow thru both valves.
    Are the valves themselves each two stage?

    The redundancy of two valves is often required.

    And having what looks like 2 ignition modules is confusing to me.
    Is there a reason for that?
    EBEBRATT-Ed Member Posts: 15,517
    Usuall 1 valve is on-off and the other valve is hi-low

    Can't see what model boiler that is must have multiple pilots with 2 ignition controls