hotwater problem heat line c24 boiler?

I have a heatline viso 24 boiler and recently the hot water has started coming out slowly . I have checked the cold water feed filter I t is clean . I have taken off the secondary heat exchanger and that was clean on the hot water side t,the boiler side was sludged up a bit but now runs freely. The water is hotter now but still runs slowly . the only thing I haven't taken off is the hytdrobloc,, I s this likely to be the cause of my problems ? cheers Baz