To do that you'll need basically your old set up refitting just for that shower, then a way of heating a cylinder. If you're using a 4 bar pump, you'll be needing a decent size cylinder to supply this also....you're already in to a decent amount of cost to do that.
Seems madness to me. Are you not just being unrealistic about the performance of the shower? Surely if the cylinder has been fitted correctly and everything else is correct - Pipe sizing, filters clean, pressure, then you'll be getting more than a decent shower out of an Unvented HW system.
I almost agree with you here. He said its perfectly normal, but its just hard when you from from an awesome shower to an OK shower. as I said, perfectly happy with the other shower and taps, it's just think one becuase of the size of the head. As i've had high expections of the shower previously in comparision, i think im just a little underwhelmed. I might post clips from the performance before and after the install.
My plumber suggested somehting similar..... I was thinking if he does it for say £2-300 i'd probably do it, as at the moment, its acceptable with no other outlets on. I've not yet tested with with say a kitchen tap and the other shower, and the washing machine on and a toilet being flashed. I imagine it would drop a fair bit! I think 100L should do it as I had 2 80L tanks before and that was fine for a few showers.