We have a sliding glass patio door that has an intermittent locking problem.

The door is locked by pulling up a paddle that locks double shoot bolts top and bottom prior to the lock being turned, i.e., it is not a mortise lock. The shoot bolt mechanism is working fine, and locks the door as it should. However, when you turn the key in the lock, although you feel it 'locking', which should prevent you from being able to turn the paddle, this sometimes does not work and you can pull down the paddle to slide the door open. The only way to lock it is to jiggle the key in and out a lot when in the locked position.

There is not a problem in turning the lock, which is a Euro Cylinder lock, and you can feel the cam in the lock turn. We thought perhaps the lock cam might be worn so have put in a new cylinder lock (easy enough). However, the problem still persists.

There is nothing wrong with the locking mechanism as when you pull the paddle up, the top and bottom bolts engage and the door is locked. There are no locking mechanisms on the door frame, just a plain white strip on plastic top to bottom. The locking mechanism are the top and bottom bolts, which are fully operational.

 

First thing I would do is lubricate all the moving parts of the lock, using a PFTE spray. WD-40 makes a PFTE "dry lube" spray that works well. Do not use plain WD-40 and do not use anything oily.

You likely have tumblers that are just a little sticky. Just squirt it right in the key hole, insert the key, pull it out and repeat a couple times.

 

Perhaps GlobalLocky will chime in, as he's more familiar with Euro type locks. It would seem that the worn or defective part is in the main lock body; sometimes lack of lubrication will prevent spring loaded "over-center" linkages from going completely over center and locking in place....by removing the profile cylinder you might be able to use the spout/application tube of a liquid penetrating lube to direct the spray into the heart of the mechanism. If this doesn't cure the problem, you'll have to take it apart....we see similar types of multi-point locks here on our side of the pond, what we refer to as "Atrium" doors, and the locks of some brands are stamped together at the factory, and not designed to be serviced.

 

Already tried the WD40. Thanks for the tip on what the door might be called, although Googling Atrium door, suggests they only lock from one side? Our door can be locked from inside or out. Looking at the coding on the side of the frame where the glass is, it looks like the doors were installed in 2007, if that is any help. We have also managed to find an image, similar to our doors:
https://www.supremewindows.com/wp-co.../07/840340.jpg

 

Have you checked for a brand name, perhaps in one of the extreme corners of the glass, for a decal, or similar? Might be helpful.

 

sound to me like a worn cam on the Euro cylinder and/or a worn locking bar inside the mechanism.
perhaps a replacement Euro Cylinder is in order?