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Wrong mixing valve? I don't see my error...

fatty_2 Member Posts: 54
I hooked up this mixing station feeding a radiant slab from a traditional cast iron system. I can only get the loop to cycle and not feed from the supply (unless i throttle the ball valve in the center)

I have never used a mixing valve in this fashion... although the diagrams in the literature show A + B to AB or AB to A + B ... I ASSUMED I could flow A to B and have just some A to AB. Wow... let's just go to the pictures.

Can this V135A (Honeywell) work?

Many thanks,

Forever a grasshopper,



  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506

    From loop to AB.....to boiler...A......up to the mixing tee...B

    Or, put it at the tee above the ball valve, then from boiler A...to loop AB....from loop..B

    Also, rotate circ so motor isn't on top
  • Paul48
    Paul48 Member Posts: 4,469
    Mixing Valve

    You circulate out of "AB" to the radiant. The return from radiant tees to "B" and to the boiler. Steve...let me know if I'm wrong.
  • Gordan
    Gordan Member Posts: 891
    How to fix

    1) Move the check valve to the return, just before the shut-off valve on the right. Make sure the arrow points to the right.

    2) Move the circulator to the supply and turn the flanges 90 degrees; the motor must be in a horizontal orientation or the bearings will go. I'm presuming that the circulator has an integral flow check.

    3) Where the mixing valve is now, put a tee.

    4) The mixing valve gets moved to the middle of the bypass, where you currently have what should be the supply shut-off valve. The shut-off valve gets moved to where you currently have the check valve.

    5) Mixing valve: inlet A points up and gets connected to the supply (replace the upper tee with an elbow), inlet B points down and gets connected to the bull of the return tee, outlet (AB) points toward the zone supply and gets connected to the circulator inlet. Place the circulator so there is a decent length of straight pipe on either end of it.

    No, none of these are optional.
  • fatty_2
    fatty_2 Member Posts: 54

    Many thanks to you guys. Especially you Gordon. I like details told straight.

    This was a system I had built years ago. It sat in an unfinished home and was eventually all torn out by thieves. A friend of mine ended up buying the house recently. Since I laid the slabs, pex, and everything myself, I volunteered to make it whole again - pro bono.

    So many years had gone by I forgot my design... in fact I forgot a whole lot. There never was anyone for me to learn from around here. Dan's books and this website were the only place I could really look to. Nobody I could learn from had a job and the rest had nothing to teach me.

    I finished it today and had it working beautifully thanks to you guys. 'Best plumbers' where I live (a rough part of Philadelphia) did all the re-spuds on the cast iron rads, while they were there they took one look at it and said "The hell's this?'

    Got a message from my friends as well... they will never go back... to cold feet.
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