it is possible your mechanism has broken at the locking point (door handle ) this connects to the multi lock and as you push the handle up it pushes a bar up for the top lock and down for the bottom. if the bar has been seperated from the centre lock you may need have it looked at by someone that knows what they are doing, or you can try lifting the door as you try to open it as the door may have dropped slightly and the bottom mechanism may not be clearing the catch, this is not a major problem and can be easily fixed although i am assuming that it is an adjustment problem
regards (window and door fitter) bob
