I bought a gorgeous bath tap with a single joystick lever for hot and cold
water, but I didn't realise that because it's a fancy-schmantzy European
thing it doesn't work well on my UK gravity system. So it takes forever to
fill the bath with hot water; the hot water merely trickles out.

In the bathroom airing cupboard is a cylinder hot water tank with the cold
water tank combined on top of it. The boiler is in the kitchen downstairs.

I'm now replacing the old boiler with a combi boiler, to be installed in the
airing cupboard. However, I've read on the FAQs that combi boilers give a
very slow flow to the bath.

My question is: Will a combi boiler make my bathroom tap even worse?

Thanks.