It's a Dorma size 3-4 overhead door closer on a 24 inch FD30 door. And I set it to close but after a couple of days it's either slamming the door or doesn't have enough force to close the door. I thought it was the door closer so I replaced it ( it was originally a Briton of similar standard) but it isn't, both door closers have done exactly the same thing. Both have been fitted using the template provided by the manufacturer. There is a bedroom directly above the door and it's causing problems. Can anybody help please?