glowworm 30ci?

Check for a second isolating valve either before or after the filling loop.
If that valve is closed, it will prevent the filling loop recieving cold water feed, or passing water into the boiler.
Be sure to shut it again at 1bar of cold water pressure, to allow expansion when the water is hot.
Most boilers are efficient at about 1.5 to 2 bar when hot.
Good luck.

Northern Knight
February 2010