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Brad White
Brad White Member Posts: 2,398
I suspect that the circulator is upstream of the expansion tank connection. This will enforce a possible negative (sub-atmospheric) pressure upstream of the circulator and will, you know, suck wind.

If a system at 20 lbs. pressure eventually settles at 12 lbs. I suspect a leak somewhere. It well could be that the relief valve has let loose and the automatic fill valve has corrected it. If this is the case, (and no other leak possibilities), I suspect that you need more expansion tank capacity.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

-Ernie White, my Dad


  • ED_45
    ED_45 Member Posts: 16
    Radiator Problem

    I have column type radiators in a forced hot water system. Early spring noticed htx 60 was defective and changed it. Simultaneously was getting knocking in some radiators which i couldnt stop. Before turning the heat on this fall I bled all the radiators with 1/8 coin vent and 1 second floor radiator will not pass either water or air. I'm assuming there is air binding that radiator. Now what do i do/
  • Eric Johnson
    Eric Johnson Member Posts: 174
    Check the bleeder

    Sounds like it may be blocked.

    I have a couple of radiators at the end of the line on my second floor that usually can't get enough pressure to bleed. I've even had them suck air when I opened the bleeder. What I finally did was to bump the pressure in the system up from 12 psi to around 20, and that provided enough pressure to vent the rads. Eventually it settles back to 12.
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