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Slow condensate return

New customer with boiler that continued to flood all last year. Will be replacing leaking VXT-120 this week. Old unit leaking and corroded.
Last spring on my first visit, to repair leaking radiator feed,customer stated he had been draining boiler once a week. Half the building heats other loop will only heat after return fully drains.
My question now is any options to get returns cleaned out without disassembling? Replacement gas boiler appears to be installed correctly.


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    Is it steam?
    Is this one-pipe parallel return, or counterflow?
    I’m puzzled by the effect of a blocked return on the steam distribution for one section. Are the main vents adequate? Sometimes, when they are plugged, air cannot get back in, and the resulting vacuum at burner shutdown can hold the water up in the vertical section of the returns-sometimes high enough to cover the main vent. See if when you remove the vent, the return flows better.
    Does the boiler overfill?
    It may be better to disassemble, and redo the returns with some tee’s so they can be rodded out in the future.—NBC
  • mikestooneat
    mikestooneat Member Posts: 12
    hi Nicholas, couple of additional comments. I did replace one one main vent and boiler was flooding. draining every week.
    Large main teeing off to radiators with individual traps. (all new from boiler install.) At end of run vent with return back to boiler.
    When I get there this week to do control I have one more return to check for pitch. Not sure what type piping system is installed.
  • Jamie Hall
    Jamie Hall Member Posts: 23,436
    Your mention of traps leads me to assume that this is a two pipe system. Before I go romping off too far into the shrubbery, though, does it have wet returns in addition to the dry returns?

    If there are wet returns -- the pitch of which is irrelevant, so long as they stay below the boiler water line -- one of them may be badly clogged or even plugged almost completely. That would be a good starting point. Then you should remember that the dry returns also need functioning vents -- as large or larger than the steam main vents. This is sometimes overlooked.

    Going back to the wet returns -- note the comment that they must stay below the water line. If there is a location where there are drips from the steam main and from the dry return, and at that location the wet return isn't reliably wet any more (not uncommon with a boiler replacement) the steam will zip around from the main into the dry return, and heating will be poor if it works at all. So check the elevation of those wet returns.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mikestooneat
    mikestooneat Member Posts: 12
    Thank you Jamie, I have a few things to check now.
  • mikestooneat
    mikestooneat Member Posts: 12
    Update on system operation. First electric feed valve was set incorrect. Went thru setup level now stable. Also found hidden main vent leaking. Wet return was full of sludge but not plugged.
    System heating even and quiet. Thanks for the imput much appreciated.