DETAILED ANSWER · UPVC DOORS AND MECHANISMS
Does a stiff UPVC handle always mean the lock needs replacing?
Understand common symptoms across cylinders, handles and multipoint locks.
No. Resistance may come from door alignment, pressure on the locking points, a dry or worn mechanism, or a handle fault. Replacing the whole lock without identifying the cause may not solve it.
Note when the stiffness occurs and avoid repeatedly forcing it. A repairer can check the door, cylinder and mechanism together. Note exactly when the handle is stiff: with the door open, with it closed, or both.
If it is smooth when open and tight when closed, the door may be pressing on the locking points. If it binds in both positions, the handle or mechanism may need examination. These are clues only.
Do not lubricate or dismantle the mechanism without the manufacturer's instructions.