I am planning to install an open vented twin coil indirect hot water vessel with solar evacuation tube panels on the lower coil and heating water on the upper coil. Looking at the best products on the market, I have looked at Heatrae Sadia Megalife solar with a Baxi Solarflo kit and it works out quite expensive. So looking at an alternative, Worcester Bosch do a Greenstore TC-250 with a Greenskies 2X Solarlux 6 kit. I questioned Worcester Bosch because the Greenstore is advertised as an unvented Cylinder. But all of the safety kit is external to the cylinder. So if I forget the expansion vessel and safety devices, in essence I could use the Cylinder as an open vented unit. The guy at Worcester was a little vague but did not think it was a problem. Has anyone on here got any views on this before I charge headlong into this project. PS: I can't have it as an unvented because of low water pressure and I don't want to install break cistern and pump or an accumulator.