I don't see a huge difference between the complexity of a low loss header and a plate heat exchanger. Both require a boiler pump and a separate CH pump. With a 4-pipe boiler like the Veissmann (with internal diverter valve), would the DHW circuit typically be on the boiler side of the CH plate heat exchanger?
I quite like the idea of having the boiler, hot water cylinder and plate heat exchanger on a sealed circuit and the mix of old pipes and radiators on an existing open-vented circuit.
I quite like the idea of having the boiler, hot water cylinder and plate heat exchanger on a sealed circuit and the mix of old pipes and radiators on an existing open-vented circuit.