Hi Carol I am not a plumber but ,have done a lot of plumbing in my own house,with help and guidance from friends in the trade,and every time I would work on something I would have to clean the screens on every tap.Your house is twice as old as mine so I can picture the deposits in the old pipes,if the pipes are original to the house.I changed all my galv pipe to copper and had to clean the screens of all the copper bits left in the pipes.Try it.Your plumber should have mentioned this.Hope that is the answer. Luck