Thanks to all for their replies.Even Hi-Spec.
gas4you. No there isn't a pump on the hot water system.
The hot water circuit runs like this. Cold water storage tank in the loft (which is now 18 inches lower down after I moved it out towards the eves), from there new 22mm pipe around loft...
I have moved my cold water storage tank and re-routed the hot water pipe running across the centre of my loft, so that I could leave the central area clear and it could be boarded out.
After the job was done I was left with one problem. If I run the hot water taps too fast, air is dragged...