If your upvc door won t lock even when still open this is usually because of the following reasons.
Upvc door lock stuck open.
Upvc door won t lock even when open.
New door necessary if unable to open upvc lock.
Problem with lock cylinder.
Upvc gearbox failure most common.
A gap between the window and the frame could also lead to draughts and damp.
If your upvc window lock is broken it is wise to ask a professional window fitter to take a look at it most upvc windows are fitted with an espag lock which is operated using the handle.
If your upvc window is open and you are unable to lock it your home is not secure.
Multipoint lock is damaged.
Especially if your upvc door lock mechanism is sticking it s usually down to the fact that you have an old door which needs replacing.
There are many types of multi point lock on the market used in upvc composite doors so hard to tell without looking most likely a fault with multi point and could be any of the components deadbolt shoot bolt etc etc undoing hinge screws may work if you can get to them flag hinge which is unlikely if they have a grub screw holding the cover in place pins could be removed if a older door.
Upvc gearbox failure or multipoint lock damage.
You ll have to call a locksmith to carry out upvc door lock repairs or potentially even replace the door entirely depending on the cause of the jammed lock.