correct water pressure in a vaillant turbotec central heating gas boiler?

i have a vaillant gas central heating system with 10 radiators and i was wondering what would be the correct pressure to have in the system to get the best heating in the house ?

the rooms are all on the ground floor and when i turn on the system only some of the radiators will get hot right now so i think the system might need more water..

The pressure is currently at 1.1 bar, and goes up to 1-.4 bar when i turn on the system..