Boiler = Worcester 9.6 ( about 15yrs old). When my hot water tap is turned on, the water now only flows at it normal rate for about 10secs before the flow is reduced to about half it normal. This is the kitchen tap, the bathroom (on same floor) the flow is less still. The CH works fine,the cw pressure appears fine and the boiler starts as normal and again appears to be fine in ever other way. Any ideas please?????