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.

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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.