We are in the process of upgrading our heating system and are considering moving our DHW cylinder from the second floor of our house to the ground floor. The system is an indirect open vented system. Based on the laws of gravity and head of water requirements can this be done without adding a booster pump to the system to keep my upper floor pressure as it is now? I have attached a crude diagram to illustrate

I agree. Won't make much difference to the pressure.

As drawn it will take longer for the hot water to come through to the outlets. For example to get to the outlet on the ground floor it has to go up to the top of the house and back down.

Perhaps this is possible...

Thanks folks for your comments i had ruled out mains supply cylinder only for the simple reason of no back up if supply is interupted.... I might actually rethink this as the mains pressure is better than my present hot water pressure frommy tank. See additional dawing showing new "Pea Coal" boliler that i am having installed the only reason i was going to move my cylinder was to have it directly on the primary loop from the boliler to utilise the recovery time of hot water depletion.I like the spec of the megaflo. (Present tank 114l new tank will be 300l.....7 people in this house!

Yes go for the Unvented, we don't get water cuts enough to worry about it.

Connect from the closest to keep the runs as short as possible.

You also need to re-think the heating, as you show it is wrong and the rads will be bet hot when the boiler is on, summer and winter.