No Hot Water ?

Hello.
I have an Economy 7 heating system and thought it would be a good idea to change the kitchen sink which meant turning off the hot water but to do so I think it emptied the cylinder tank as it took a long time for the hot water to stop running.
My problem now is I have no idea why the cylinder tank is not refilling and their is no pressure whatsoever ?
Header tank in loft is full.

Help Please

Hazel
May 2010