The DIY thread - DIYourself

[Mahnken]

Is there another pump upstream on the hot? Maybe part of the boiler?

I could see this being a hydraulic separator?

I get the idea that it mixes the return cold,
(I looked multiple times today, since I did a picture search it landed in my feeds) just seems like it's own loop

Yea, there's a bigger main circulator for the boiler, then five of those isotherm zones with their own pumps