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  1. #1

    Air in a closed loop system

    Hi, can anyone explain how air gets into a closed loop heating system?


  2. #2
    Join Date
    Aug 2007
    Northern VA 38 degrees N by 76 degrees W
    Quote Originally Posted by geochurchi View Post
    Hi, can anyone explain how air gets into a closed loop heating system?

    As in a boiler system?

  3. #3
    Join Date
    Feb 2010
    In a boiler room
    If there is a leak somewhere, or the relief valve is intermittently discharging. The fresh make up water brings in oxygen which turns into bubbles.

    Also if you have an automatic air vent in a place that sometimes sees negative gauge pressure. This can happen if system is not piped correctly.

  4. #4
    Join Date
    May 2005

    I agree...

    I've seen auto air vents misapplied on the 3rd floor of a building that were sucking air into the system !

    If your working in a multi-story building, make sure you have about 5 psi at the highest floor...

    Good luck, stay safe,
    I may not be the sharpest knife in the drawer, but compared to some I'm a razor...

  5. #5
    Join Date
    May 2012
    Upper Michigan
    Without any other info it's hard to say, but there is no way unless there's a way, air vent, leak, low pressure, relief popped and maybe no water feed.

  6. #6
    Join Date
    May 2004
    Rapid City, SD
    Don't forget to check the expansion tank also.

    If you have the old style air over water tank (everything in one tank), sometimes an air vent that's really good can pull the air out of there too from a long ways away in the system.

    If you have a bladder tank, make sure it's still hollow sounding.

    Not a whole lot that can introduce air into a system, but on the other hand, air in the system can sure make you pull your hair out.

    I had a 5 story building I accidentally got some air into. You'd think it would have just settled out in the top floor... but it didn't. Seems like most of the air was in the 3rd floor, and hardly any in 5th.
    "If you call that hard work, a koala’s life would look heroic."

  7. #7
    Join Date
    Aug 2011
    Salem Oregon
    Do you have any Pex pipe in the system? It has to be bought with a specific coating for heating systems. Often it's a red color. The polyethylene itself is oxygen permeable.

  8. #8
    Join Date
    Jul 2010
    What is the pressure on the inlet side of the pump? Pres reg valve setting (12psi)? if the pump inlet pressure drops below the vapor point the water will vaporize, no air injection needed.
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