I just went round 2 radiators bleeding the air out of them. On the 2nd
there wasn't much air at all coming out. On checking the combi boiler, the
pressure bar has fallen to 0. It was only just over 1 to begin with.

What do I do now? Will it top up automatically somehow?
How do I do it myself?
Is it unwise/dangerous to put the CH back on now? What about using hot
water?

Help!