Without proper maintenance, the lock can become dry and sticky. Cleaning it fully and applying lubricant will make it as good as new. When the key is difficult to insert or impossible to turn, it means the Euro cylinder has most likely failed. It has to be changed so that the lock can work properly again. A jammed bolt or hook is another fairly common problem affecting UPVC door locks. If a rubber seal has got into the way, it has to be removed carefully and a new one has to be installed afterwards. If the loose strike receiver was the part that had caused the jamming, it should be adjusted securely in place. Tightening the screws is essential. If a screw is missing, it should be replaced. If the handle is loose or the lock is stuck despite a smooth turning key, the locking mechanism is most likely broken and should be replaced.
The lock may not operate smoothly because the door and frame don’t fit accurately. You will be able to see the misalignment between the mitres very clearly. Adjusting the hinges should help to solve the problem. A special tool is inserted into the screw of every hinge and turned into the required direction. The position of the door is regulated with the number of turns. Only hinges in perfect condition can be adjusted. If they are greatly damaged, worn or broken, they should be replaced with new ones to align the door properly. If rubber seals prevent proper fitting of the door into the frame, they should be replaced too.