I am in the process of replacing my HW & CH programmer. The current Siemens RBW9 unit has the dip switch (5) set as gravity fed. However, I have a grundfoss pump and what I believe to be a Y-plan system with a three way valve, hot water cylinder in the airing cupboard with a cold water tank and small expansion tank in the loft. Please could someone confirm if it is fully pumped as I suspect and if so the difference in terms of operation with it having been set to gravity please? Photos below of the airing cupboard arrangement in case it helps.