Hot Water Pressure?

Hi all,

I have a combi boiler that is heating cold water for the hot taps as and when there is a demand for it. Do not have a hot water storage tank. Its all heated when i need it.

I have a problem in that i dont seem to have enough hot water pressure. The cold taps are all fine. However if i turn on the hot water tap upstairs if i turn on a hot water tap down stairs the pressure upstairs drops to a mere trickle. If i turn the cold water on it virtually stops altogether.

It was never a problem before and seems to be getting worse. The water board came out to check the cold water pressure both in the street and in house. All checks fine. Should there be a setting on the boiler to increase the hot water pressure.