I have a front upvc door which has a mortice lock and bolts which operate when you turn the handle up.But unless you lock the door it can be opened from the outside, is it possible to fit a night latch to these doors.
Don't even try to fit a nightlatch as it wont work. Some of these multipoint mechs can actually be converted to open and close like a night latch does. Im assuming it is a new build it is on ? Try inserting the key from outside and does it withdraw the latch if you turn it far enough ?
If it does withdraw the latch then you may be able to convert the lock. You need something called a split spindle setup.
Although its quite an easy thing to do its probably outside the realms of a diy job if you not done it before.The last thing you want is to get locked out because you haven't done it right.
If you can send me a pm i can point you in the direction of a locksmith in your area who could do this for you.