Ive just rang her and she's topped it up using the filling loop. It was
nearly on empty. Tomorow I shall bleed her rads for her. Is it positive
that I bleed with the pump pumping water round the rads? mr J

It matters little on a sealed system at 1 bar pressure, although it is safer
off, as any water spray will be cold. On a gravity system, you need to turn
it off, as the pressure within the pipework can be sub ambient pressure, so
it sucks air in.

Christian.