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What is this (mixing system on vintage PEX hydronic manifold)?

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wvukidsdoc
wvukidsdoc Member Posts: 3
in Radiant Heating

So in preparation for laying out a new system at my father‘s house, I am trying to understand some of the old system. Dad installed this assembly somewhere around 1995 to 2000. He did not build this assembly himself, bought it from a early online supplier. This assembly “failed him about 15 years ago, with him thinking the three-way mixing valve failed, but honestly, it could be the pump or control system as well. Up until that time he states the assembly was regulating the temperature to the under floor PEX he had installed in a new addition, and added to the floors of old areas. At some point “it died” and for 10+ years has a bypass hose somewhat randomly mixing from a port closer to the return side of the boiler. Mind you for context, the boiler circulator is circulating to the entire house through zone valves, this is not primary secondary unless somewhat unintentionally. Again, I do not know what has failed, if the circulator even still runs, if it was inadvertently acting as a system circulator, or only for mixing. I’m trying first to understand exactly what is going on here as it was initially sold/intended. It would seem to me that the circulator here, possibly variable speed, has a control (the orange dial has temperatures in centigrade) as the mixing device. If so, what is the three-way mixing valve doing? I thought for a second it might be intended for boiler return temperature protection, but the outlet isn’t going in that direction, is rather feeding back into the manifold. I actually tried Google lens to see if I could even find a similar picture to the control to know what/who made it but alas, being from the early days of the Internet, no luck. I am unfortunately 10+ hours away, dad really can’t get to this anymore, he broke his femur last year, ended up with a short leg. My sister sent me pictures and video last weekend. I’ve bought the new boiler, and want to have most everything together before I go down for two weeks. For context, right side beyond the shut offs going to supply and return to the boiler, left side is just 5 loop PEX hydronic manifold set. Also for context, despite dad saying it did, this may never have truly “worked.”

IMG_1662.png

TIA to anyone that can tell me what was initially going on here. Again, I used to be a mechanical engineer, but gave that up about 20 years ago. So I’m only partially an idiot.

John

Comments

  • mattmia2
    mattmia2 Member Posts: 17,752

    The gray box with the orange knob is probably an aquastat. The 3 port valve with the knob is a thermostatic mixing valve. My guess is when the piping is hot because of a heat call the aquastat turns on the radiant loop circulator that moves flow through the mixing valve pulling some from the radiant returns and some from the boiler based on what the mixing valve senses to make the low temp water for the radiant. One of those 3 parts has failed or isn't getting power.

    If you are using a mod con boiler and have no high temp loads you can make low temp water directly from the boiler and eliminate the mixing. You could also do outdoor reset that way.

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