System very slow to re-fill?

Hi, this is a great site and my first post, i have a slight problem, hopefully someone will be able to help me out to sort it:

i have drained down my whole heating/hw system this morning, to fit a new radiator as the old one was rusting and dripping. that was all done fine.

the problem is, when re-filling it seems to be taking ages, and no water from the top radiators yet.

i have a header tank which i tied up the ballvalve arm and have released again to re-fill the system.

is there anyway i can shift the what seems, air in the system, to allow the system to fully fill up again soon??

why is it doing this-was my system just installed/designed badly??
i have lived in this house for 6 years and the system was here when i moved in.

any ideas please?

It sounds like you need to open the 3 way valve to allow water in to the whole system.

the 3 port was open (mid pos).