it sounds like you may have a build up of limescale,you could try undoing hot tap and see if will flush through,but prepare for amess,or you could have to drain hot water cylinder and cut anew length of pipe running from bath to sink you can use 22mm copper or plastic pushfit fittings coupler and pipe,but check the size of the old pipes.hope that helps you.best o luck
alz
July 2004