No Hot Water OPTIMA 701 gas combi boiler?

I get no hot water unless I have the heating on. I have cleaned the water filter, flowmeter and flow restrictor. This cured the problem but for a short time only. I did find sediment in the water supply so I flushed the boiler out by removing the blank plug on the domestic hot water outlet.
My local plumber suggests a new boiler.
I need some proper advice ?

James Roberts
September 2007