Heating system won't fill

[JoeRoberts]

When I open the valve in the hot press to bring the pressure up, no water is flowing in.
Has been no problem in previous years, just open and watch the gauge rise . Any ideas ?
Have bled the rads, pressure is almost zero so needs water.

 

[newtothis]

A stuck valve somewhere? Similar problem happened to me recently, and it turned out to be a faulty valve I wasn't aware was even there - one of the ones that automatically opens when pressure drops (only in this case it didn't).

 

[Seagull]

We have a filler loop with valves at both ends for topping up the heating system. Is it possible you also have this, and someone closed both valves, and you're only opening one?