Getting rid of flies

My third-floor apartment has a balcony, the door to which I can never open because there's always a gang of flies hanging about threateningly outside the door, waiting for their opportunity to storm my house.
I've taken a look around the balcony and there's nothing on it or over it that would attract them - no plants, food, rubbish, nothing. There's an overhanging roof but that's it. Anyway, I don't particularly want to kill them but every time I open the door loads of them fly in and they're pretty disgusting. They look like ordinary house flies. Does anyone have any advice on how to keep them away from my balcony or at least out of the apartment? I've tried spraying the door with fly spray but it's not working.

You could try Citronella candles or burning Citronella oil in an outdoor burner on the balcony, we have the same problem at the moment and it's working to a certain extent for us. You can get these in any DIY shop, even Dunnes and Aldi have them.

Aldi also did a special recently on fly curtains for doorways and UV-lamp type fly zappers, I have one of the latter and it worls very well. They may still have them in stock. Flies are attracted to light, so if there is an overhead light outside you door that may be all that is attracting them. Also, any puddles of moisture on that flat roof will also attract thirsty flies.

I wonder could those UV light be used for midges - they are horrendous around my place - so much so you can't go outside after 7pm for fear of being eaten alive!!!!!

Not sure if its the same situation but i used to have a room with velux windows in the roof but the windows werent opened very often and at a certain time of the year every time the window was opened, loads of flies would drop in the window. They seemed to be hibernating or breeding around the edges of the window. We tried spraying fly spray around the window too but it didnt work, there would just be more the next time. What seemed to solve it was opening the windows every day or several times a day and they dont hang around.
if this is the problem, not opening the door might be adding to it.

I'll give it a try - just terrified I'll arrive home to a mini universe of flies in my living room. I'll get that citronella stuff too - not sure I could handle the guilt of them flying into a certain, burny death in that light thing.
Thanks amillion, I'll let you know how I get on!