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No flow - pressure issue

40*32 pole barn - 3 loops (200ft/ea) - wood boiler (closed system).

Everything setup and used last year. Had to do some re-plumbing before use this year. As I'm getting things setup initially and purging my system I wasn't paying attention and hit 30psi and the blow off valve opened (no heat during this). Didn't finish. Came back to it and I've tried bleeding my system and can't get above 12ish psi. Maybe 15psi tops. 

I have my pump above the boiler, running down to my manifold, through the loops, to my return manifold. Valve closing off return manifold to boiler return. Return manifold drain open, hose running to boiler for constant supply. Opening and closing one loop at a time. Ran each loop 10-15min. Obviously no pressure on boiler gauge when purging, but I also closed the return drain and kept the water flowing into the boiler and pressure never got above about 13psi. Flow meters don't change while purging or running system closed, but I can here the check valves or whatever is built into the zone meters click when they're opened.

My supply manifold is a couple inches lower than my return manifold. Never had an issue with it but figured I'd ask if thats an issue since every setup I've seen shows the opposite. flow meters on supply, valves on return. 



  • Jamie Hall
    Jamie Hall Member Posts: 22,213
    What pump are you using for all this? Keep in mind that all centrifugal pumps -- and circulators -- have a characteristic performance curve, and if the flow increases the pressure falls. The pump, under any given condition will come to a certain flow value at a certain pressure, depending on the pump curve and the system head curve and just sit there.

    Now if you increase the system resistance -- partly close a valve or add lengths of pipe -- the pressure at the pump will rise and the flow will drop. If you stop the flow entirely -- close a valve -- the pressure at the pump will rise to the pump's shutoff head, and never go above that.

    From most of your description it sounds to me as though you have an open drain at one end and are pumping into the other. The part which baffles me is where you say you change to pumping into the boiler -- without a drain from the boiler? -- and the pressure should rise.

    Further, as you open and close things, the flow should change.

    So I'm puzzled. I'm also a little worried that you have a significant leak somewhere...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 20,836
    only 600' of tubing in a 1200 sq ft shop?
    So the circ is not moving flow, is that the issue?
    can you attach some pics of the boiler piping?

    What piping changes were made?
    Does the boiler heat any other buildings?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • leonz
    leonz Member Posts: 970
    Do you have a bladder expansion tank or steel compression tank with an airtrol valve and an Internal Air Separator.

    If you do not have a bladder expansion tank with an air scoop or steel compression tank above the boiler you have no point of pressure change and that would explain it all.