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Hot water heating banging pipes

Jas29 Member Posts: 3
Having some ongoing issues with the heating system in my parents house where the pipes continue to bang even after removing the air from the system. Recently they had the air separator replaced which didn’t help. 

Also how do you decide if the pump should be on low, med or high as per my dad the plumber left it on high with the bypass 75% open as they said the water should circulate even when the pump isn’t needed 

I have closed the bypass majority of the way and lowered the pump to med and the house is still getting heat evenly 


  • Intplm.
    Intplm. Member Posts: 2,084
    A bypass on the boiler? From the feed to return as seen in the picture?
    Shut that valve all the way off and leave it that way.

    Your "air separator" as you call it is not an air separator that appears to be installed on the top of your air scoop.
    A true air separator should be installed instead of the air scoop. The air scoop is also installed incorrectly.

    But lets not get ahead of our selves.
    What does the gauge pressure say? It should be 12-15psi.
    I'm guessing from here that you have air in your system. Too much air for the air scoop or the new looking high hat air vent that has been installed on top of the air scoop to eliminate.
    I'm hoping you have a manual purge set up on the return side of your boiler.
    This is where you need to purge your boiler from the trapped air.
  • bburd
    bburd Member Posts: 935
    What type of radiators do you have? Copper fin tube or old-fashioned cast-iron?

  • Jas29
    Jas29 Member Posts: 3
    Yea the copper pipe behind the boiler that goes back to the return side was left mostly open.  

    The plumber called it a air separator just going with what they said. 

    There is no pressure gauge on the system and the temp gauge is also broken hoping I can get a 2 in one gauge that will be pressure and temperature. 

    Yes there is a manual purge on the other side. 

    Radiators are copper fin tube 
  • Gilmorrie
    Gilmorrie Member Posts: 185
    The "banging" may be caused by thermal expansion of the pipes - causing them to rub against wooden joists. If that's it, there may be some fixes if the offending pipes are accessible.
    HVACNUT Member Posts: 5,890
    It's got a fixed speed circulator. If 2 zones are simultaneously calling for heat, then one zone satisfies and its zone valve slams shut, there will be some hammering going on. 
    Does that seem like what's going on, or is it a constant banging?
    If it is hammer when a zone valve closes, that's why the bypass is there. Having a ball to regulate flow is a poor choice at best, but if you open it about 45° (or half way) I bet the hammer goes away. 
    There's better ways to handle it, but a lot more intrusive. 

  • Jas29
    Jas29 Member Posts: 3
    There is for sure air in the system they said every time they get it purged it’s okay for awhile. The bypass was open more before I closed it most of the way and lowered the pump speed to “medium”

    seems like the air scoop isn’t installed in the correct position and not doing it’s job 
  • Big Ed_4
    Big Ed_4 Member Posts: 2,835
    I would say the boiler could be breaking steam . But without a tridicator gauge , how would you know ...

    If the banging has a snap , it would be steam ...

    There was an error rendering this rich post.

  • fentonc
    fentonc Member Posts: 241
    @HVACNUT - Probably not a great solution in this case, but I added a little PLC that sits between my three thermostats and the zone valves, and it temporarily inhibits the circulator while a zone valve closes. No banging so far!