change of hot water pressure

Hi, my water pressure in both hot and cold have reduced to nearly a trickle it was ok in the morning but now really low. The hot water is from a tank upstairs heated by central heating bolier (open system) anyone any ideas why this has hapened and what i can do to fix it? thanks for your help

Here on this side of the pond our systems are quite different than yours.
It might be a while before a plumber familiar with UK systems chimes in...
You probably would get faster answers at this link...
http://www.ultimatehandyman.co.uk/forum1/index.php
We're helpful kinda guys but as I stated way different systems...

Thanks

Thanks Guys it was a blocked airater