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Problems caused by airlock in hydronic heating systems

We recently did a large scale replacement of the zone valves in our apartment complex. When we watched the contractor doing the work, we noticed that they did not do anything to bleed air from the system after installing each zone valve. Our staff later had to go back and bleed the air out of the heating lines. Before we were able to do this, however, we had a number of problems with freeze-ups in the system as well as with no-heat calls in apartments. Is it possible that airlocks in the system could have contributed to these freeze-ups by preventing the hot water from flowing through the apartments?

Thanks for your help!

Comments

  • STEVEN MARKS
    STEVEN MARKS Member Posts: 154
    Air

    Yes, air can prevent the circulator from moving water. If the zone or cedtion of heat is air bound the circulator is not moving the water thru the boiler. That zone or section of heat can than freeze and burst.
  • Eric Johnson
    Eric Johnson Member Posts: 174
    black art

    My daddy, who started up power plants for a living, always described system venting as a "black art."

    Somebody told me once that on hot water heating systems, it always pays to put in a manual vent or cast iron plug any place a return line heads down. Is that a good rule of thumb?
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Vent all High Points, Drain all Low Points

    is how our specifications read.

    An exception would be a single series loop circuit which could be purged. Still, a high vent is a good thing.
  • Eric Johnson
    Eric Johnson Member Posts: 174


    In my limited experience, it's a lot easier to put them initially than have to go back and start adding vents when you discover there's no flow.
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