DETAILED ANSWER · UPVC DOORS AND MECHANISMS
Why does the door handle lift but the key won't turn?
Understand common symptoms across cylinders, handles and multipoint locks.
The handle can move the multipoint strip while the key and cylinder operate a separate part of the system. A stiff cylinder, misalignment, or a mechanism fault may prevent the key from turning. Do not force the key or use pliers.
Note whether the handle moves freely and whether the problem occurs with the door open, then share that information with a repairer. A useful distinction is whether the key itself resists turning or whether it turns but does not secure the door. The first can involve the cylinder; the second can involve the cam, gearbox or multipoint mechanism.
The door's alignment can still affect both. Stop before the key bends or breaks, and do not use tools to increase leverage. Share the sequence of handle and key movements with the repairer.