Trying to get my head around this system in our cafe. It's the relationship between the circulating pump and the ?bypass (above the red knob on the right) that is not making sense to me.
It just seems like the circulating pump is dragging the cold water around and around through the loops. It's doesn't look like other manifolds I've googled...
That is a typical setup for heating here in the Netherlands, I have it in my house. OP is in Germany, so probably not too different.
Edit: OP is not in Germany, but there are German stickers in the picture