Our teminology (US) for overhead roll-up doors is somewhat different than yours... probably. Let me see if I can work around that.
First, is there a disconnect handle on the chain drive? It should hang down where it's obvious. Point is, when you pull the handle it disengages the door from the chain drive (at least here). When you pull the handle the door, if properly balanced should open by itself (the spring is doing this) about half way up. Some times the spring tension requires adjustment to achieve this balance. If the door isn't balanced it sometimes can shut off (automatic safety function) as it rolls up.
By the way, if the spring isn't adjusted properly, it's best not to try to do it yourself unless you have experience or know someone who does. It can be quite dangerous (but entirely harmless if you know how.
At any rate, that's the first thing I'd do.
If it does balance correctly, go ahead and use th e remote or interior door switch to roll the door up and the disconnect handle will automatically reattach itself to the chain drive...