radiator pressure

Hi could someone please give some advice? I have removed a bedroom radiator ready for plasterer. We turned the valves, drained the rad and removed it. But then I realised we have no pressure in the boiler and it won’t let me re-pressurise as I normally would with the valve on the boiler, it just...

In my apartment the boiler (a Vaillant ecoTEC plus) wasn't working and someone came to fix it. He opened the valve to increase the pressure and now the boiler is working again but the pressure is always on the "red" region. Is this safe ? I do not see any radiator air vent to open (see image)...