Boiler was working fine on Wednesday. Got turned off on Thursday morning. Went to turn it on again Thursday night and noticed the water pressure gauge was at zero. Boiler won't start.

Found out you can bring the pressure back up by opening the filling loop for a little bit. Tried that but the gauge remained at zero despite being able to hear water running through it.

How long is it safe to keep the filling loop open? I'd like to keep it open a bit longer but I don't know if it's safe to do so or whatever.

Theo?