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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...
It seems to make no sense. The top rail is hot and the water should flow through the circuits back to the cold rail on the bottom. The pump should be in-line and not across the rails. The pipe on the right between the top and bottom rails would also seem to be defeating the purpose of the two rails, allowing water to flow from hot to cold directly. It looks like a rebuild is in order.
There is another pump that is in inline with the heater. This pump is needed to mix the hot water from the heater with circulating water from the floor heating, to have an acceptable temperature for the floor. Water directly from the heater can be too hot for floor heating.
There is something wrong with the setup if the boiler is putting out temperatures too hot for the floor heating, e.g. a radiator circuit is being used for both radiators and underfloor circuits.
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