Our external back door has started to jam when you open it and today it took a lot of brute force to get it open! When it is open you can see that turning the handle doesn't make the hooks etc go all the way back in. When it is jammed you can hear that some of them are banging against the door frame when you try to open the door. Can I fix this myself or do I need to call in someone, and if so who? The mechanism is a Mila master (if this helps!) 
