The CH pressure gauge at the megaflow was reading zero the other day (the mains pressure was reading 3 bar). So I bled some water through until it was back to 1 bar where it still is.
Still, presumably water can still be pumped around the system as the rads were getting hot as was the hot water. And downstairs, where the boiler is, it's going to be half a bar or so higher.
I can see that bleeding a rad at the high point would not be possible under that regime, but is there any other reason for keeping high point pressure around 1 bar?