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radiant flow problem

I am having trouble getting proper flow through a radiant slab. Total of six loops of 1/2" pex about 1400' of pipe. The problem is when the Honeywell AM 102 mixing valve is throttled down to anything under 125-135 degrees my flow shuts right down and even at that temp I am only getting about .5 gpm. I am thinking that the pump is under sized, but not sure? There was a 007 on and switched it out with a 00R and have it on high right now. 

Thanks in advance for any feed back.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    edited October 2011
    are you using the AM 102-1?

    I think you're using a domestic hot water mixing valve in your radiant mixing.  If that's the case, you may have it set for 130 degrees, in which case it's doing it's job.  .

    What kind of temperature are you looking for in your radiant?  Are you using outdoor reset?

    Draw a sketch, or post a pic with all the controls labeled and we'll help some more.

    quick edit..just looked it up. Says it can be used for radiant. 
  • plumbraider
    plumbraider Member Posts: 4
    Radiant flow problem

    Boiler is Laars Mascot II combi W/outdoor reset. The mixing valve is AM102, I've attached a drawing.

    Thanks again.
  • plumbraider
    plumbraider Member Posts: 4
    Another question

    Been doing some reading and it seems that I might have a problem with the way I am piped into the mixing valve. My cric is pumping into the hot side and pushing thru the mix port. Would this account for restrict when trying to temper down?
  • Gordan
    Gordan Member Posts: 891
    edited October 2011

    The circ should PULL from the mix port. The way you have it, the only pressure comes through the hot port, so when the valve throttles down on it, it's (indirectly) throttling down on the cold port, as well, which makes it throttle down more on the hot port and... well, you get the gist of it.

    Why the mixing valve, anyway, when you've got outdoor reset? That seems completely bass ackward.
  • Ironman
    Ironman Member Posts: 7,119
    Are There Any Other Circuts Connected To Your Boiler

    I ask because the way you're piping is drawn would require 3 circs. You would need one in the boiler loop; one in the primary loop; and one after the mixing valve as Gordon pointed out. And, as he also noted, you don't need the mixing valve unless there are other higher temp zones.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • plumbraider
    plumbraider Member Posts: 4

    Thanks for the help! I do infact have another zone which is high temp thats why I have the mixing valve and the outdoor reset. The Mascot II comes with a primary cric built in.
This discussion has been closed.