Air in Radiators

I have an Ideal Icos Boiler system , but i have been told conflicting stories on how to remove air from my radiators and top up the system. When I switch on the CH and bleed the air from the radiators the pressure goes down and appears that there is not enought pressure / water to have all radiators on full. It is a new system so dont think it is technical fault. One person told me that it is a closed system and will fill up with water itself , however someone told me i need to fill system from the main . I have a kitchen boiler with a hot water tank up stairs. Help please.

try a search on fill loop
or look for the silver pipe