Power Shower / Hot Water Combination Cylinder

[aber]

I would like to install a power shower without getting rid of my hot water combination cylinder (80/20). I am aware that the cold water section of the combination cylinder being 20 litres only may cause problems in terms of feeding the hot water tank in time to keep up with a power shower pump.

Would I be able to get around this problem by installing a separate cold water cistern on the loft and then feeding the cold water section of the combination tank with a direct gravity flow from the tank on the loft?

I am greatful for any ideas!! Thank you.