Hi Graeme,
I've waited all night and the pressure hasn't built up. To describe it more fully to you -
There's a cold water input pipe which goes off to the loop and also up into the boiler. The one going up into the boiler has a stopcock on it. I've tried with this open and closed. On the loop where the flexible hose is, there's a screw which seems fully open on the joint. Then comes the pressure gauge, it's showing just above 0 bar. Then the flexible pipe is connected and water seems to be going through the far end. I've checked all of the radiators and there's no leak.
Andy L
March 2008