Moah Pressure!!!

 The pressure gauge* on the boiler started working again, which let me see system pressure was about .75 bar, just about hovering on the boundary between too low and okay (well, I presume that's what the red and green circumferential lines mean). So I opened up the inlet valve and started paging through the (mostly installation) manual trying to see what it should be. This is obviously the wrong order to do things in a poorly organised manual as when I looked up, not having found the right value yet, the pressure was now 2 bar and headed for the boundary between okay and woah there!!! (I'm pretty sure there'll be a safety valve in there, but best not to trigger it).

So I went around and bled all the radiators, and yep, that was definitely pressurized! I got all of the air out of them and went back to check the pressure gauge, which was back to reading .75 bar again. *headdesk*

This time I looked up the value first, which was a helpful "between 1 and 2 bar", which I found not because it happened to be buried in the middle of a page of mostly unrelated text, but because there happened to be a diagram with the pressure gauge tagged. *rolls eyes*

Filled it more slowly this time, and it seems to be about 1.25/1.3 bar, so solidly in the green. I also went back and checked that youtube video and they suggested 1-1.5 bar, so that's finally right.

* It's the size of a £1 coin, you're not going to get a precise reading off it.