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Circulator-Mixing Valve Orientation Question

Thanks in advance for any help with this issue everyone. I love the site and have found tons of great info here over the years.

I recently installed a new WM Aqua-Balance 120C combi boiler in my 2-story 1911 craftsman. I have CI rads on the first and second floors that were running on one zone previously. As part of this project I zoned the floors separately using Taco 007 circulators and added radiant under my first floor to help heat the hardwoods.

My plan was to combine the radiant and the 1st floor rads on one zone. I installed the system and quickly found that I had very little flow in my radiant floor system. After flushing the system to remove air, pulling apart the radiant manifold to ensure the valves were working I think I've diagnosted the problem. I believe my issue lies in the orientation of my circulator pump to my radiant mixing valve. After reviewing info on this site and other internet forums I now know that the circulator should pull from the mixing valve not push into it as my system currently does.

So now on to my question. I have 2 options (maybe more) on how to fix this as outlined in the attached images.

Option 1 leaves the 007 powering the 1st floor rads and the radiant mixing valve but I then install another 007 after the mixing valve to pull flow through and then into the radiant manifold. My concern is that with circulators on both sides, the inbound flow may choke the mixing valve, not allowing cooler water to mix and achieve the right temp balance. Is this accurate?

Option 2 involves cutting in a new T to the main loop, installing the mixing valve after the exp. tank and then following it up with a 007 circulator and the radiant manifold. I think this is the more "correct" setup but it also is more involved so I'm wondering what the forum thinks of these options.

Is option 1 going to work and work well? Or should I skip the easy route and plumb this by-the-book despite it being a bit more work?

Thanks in advance for your help and expertise. And sorry for the basic drawings, spreadsheets are the best that I have.
Picture of the current setup

Drawing of the current setup

Drawing of option 1

Drawing of option 2


  • DZoro
    DZoro Member Posts: 1,048
    I'd vote for #2
  • Cold_Feet
    Cold_Feet Member Posts: 3
    Thanks for the feedback Zoro. I agree that's probably the proper fix but just wondering if you think that having circulators on both side of the mixing valve would present performance issues?
  • Ironman
    Ironman Member Posts: 7,376
    Nice workmanship, but just at a glance, there are two things that need to be changed:
    1. The circulator MUST be between the mixing valve and the manifold.
    2. That's not p/s piping with the connection between the Tees; it's just a bypass that's gonna short circuit the flow from the boiler back to it.

    I'll try to comment further when I have more time to look at it.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Cold_Feet
    Cold_Feet Member Posts: 3
    Thanks for the feedback Ironman!
    #1- I figured as much from my recent research, just wish I had done so from the get go. I currently plan to correct it via Option #2 above placing a T after the exp. tank that runs to the mixing valve and then through a circ and into the radiant manifold.

    #2- I would love to hear more about the p/s comment. I honestly don't fully understand the flow aspects and did my best to represent the info found in the boiler instruction manual. I understand the purpose of the p/s but not the flow aspects and proper placement. Is the concern the distance between the Ts or the actual placement of the p/s Ts in relation to the overall piping?

    Thanks in advance for your input!