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2 pipe steam trap systems

I have a 4 story apt. bldg. with radiator traps and no boiler return trap.  Only 1 radiator doesn't get hot on the first floor.  I changed the trap and it worked.  Next day still no heat.  So I took off the trap cap to change the disk in the Hoffman #17c and noticed the water that didn't pass the disk was bubbling.  As I removed the disk there was air shooting out the return line and after a second or two it stopped.  I then shut the radiator valve off and blew into the trap and felt like a water restriction.  Only the riser out of the return line is visible so I can't see if there is a trap in the pipes.  Since the boiler runs on ounces of pressure, and  if there is a piping trap, could that cause the air pressure built up in the pipe to stop the condensate from flowing past the radiator trap?   If not I'm open for suggestions.


Geo. Jaekel Inc.


  • Jamie Hall
    Jamie Hall Member Posts: 22,878
    It does sound...

    remarkably like there's a restriction -- or a complete blockage -- somewhere in that radiator's return line.  When one is working with ounces of pressure, it doesn't take all that much.

    If you pour water into the return (trap open), does it go away?  That is, does it drain?  That would eliminate a real blockage.  However, your suggestion of a "pipe trap" (which puts me in mind of an "S" or "P" trap pipe configuration) is also a possibility, although why a knucklehead would have done that... that would keep air at an ounce or two from leaving the radiator, which would be bad.  You'll have to trace the return line back to the wet or dry return to check that, though.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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