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I am trying to get this heating system working. Currently the hot leg between the tank and mixing valve is hot(~135 degrees). The leg between the mixing valve and circulator pump is hot(~135 degrees). The leg between the circulator pump and tank is hot(!135 degrees). The return manifold is cold(~68 degrees). This does not change regardless of the mixing valve setting. The circulator pump is running, the motor and impeller are new. The system has been bled of air and as a whole as well as each of the pex loops. The system is 3/4″ copper from the tank to each manifold then pex between manifolds. I don’t know the run of each pex.

I plan to replace the mixing valve but am confused as to the placement of the “Cold” line which is mixing returned water form the loop. As it is now (the orange dotted line) the mixing valve getting more pull down from the circulator as it is the largest and closest line. Wouldn’t it make more sense to re-plumb the return hot water to the mixing valve so that the circulator pump is both pushing water into the tank/inlet of mixing valve AND pulling water from the mix side of the mixing valve (purple dotted line)?

Thank you for your input!

Other notes: 60,000btu residential boiler. 3/4″copper lines. Open water system as laundry/shower/faucets come off this boiler and the domestic cold is plumbed into the boiler. There is a bleeder valve between the mixing valve and the hot water tank at the highest point.

EDIT: I updated the picture to reflect domestic in/out, bleed valve, and actual orientation of mixing valve.

https://preview.redd.it/l8goe5qjgbx31.png?width=1410&format=png&auto=webp&s=e48f605d56b0a92f6dec40c0d4a43440b581f683