Nobody wants to pay a locksmith to come over and fix what seems to be a simple mechanism. Most (not all) sliding glass doors feature what are called, clasp locks. The shaft sits inside the door frame and a clasp from the locking mechanism closes over the shaft when you lock it.
There are several possible reasons a sliding patio door won’t unlock, such as the lever being in the wrong position (not completely up or down), the clasp mechanism is seized, the door is frozen up (winter problem), or the mechanism is simply broken.
A clasp door lock is very common. In fact, the only other locks typically used on sliding doors are foot bolts and security bars. Once in a blue moon, you might find a genuine cylinder lock on there but it’s highly unlikely.
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What To Do When You Sliding Patio Door Won’t Unlock
The first thing you need to do is look at the lock by opening up the sliding door and flipping the clasp.
You can do this with a small screwdriver or sometimes even your finger. Now, close the door, with the clasp extended, to get an idea of where it lines up against the shaft in the door frame.
Adjust the Clasp Mechanism
You can adjust this clasp up and down a few degrees and a visual inspection will alert you if there happen to be a few loose screws around the mechanism. If there are, you should tighten them back up and see if that fixes the problem before you proceed any further.
You can adjust the lock latch throw by turning the screws clockwise or counterclockwise. There should be one screw above the clasp (latch) and one below. Usually, they are designed for flathead screwdrivers but that’s not always the case.
Remember, whatever you do to the above screw, you also need to do with the bottom screw. If you turn the top screw counterclockwise three turns, you should do the exact same for the bottom screw.
You can mess with this, back and forth, periodically testing the locking mechanism by closing the door and flipping the lever after every adjustment. Hopefully, the fault is a matter of the latch being off just the tiniest bit and the adjustments via the screws will solve the problem.
Carefully observe the strike plate as well. You may have to adjust it once you’re done with the lock mechanism.
You’d be surprised at how much moisture gets inside your sliding glass door locking mechanism. Corrosion doesn’t take long to start running the show so it’s a good idea to give a shot of non-oil-based lubricant from time to time.
The reason you should stay away from oil-based lubricants is their tendency to attract dust and other debris or material that’s light enough to float around. It’s like glossy plastic. If you’ve ever owned a device with a glossy plastic shell, you’ve probably observed the magnetic attraction to dust that the surface creates.
It’s exactly the same with oil-based lubricants. Go with something like DuPont Non-Stick Dry Film Lubricant or the Dry Lube version of WD-40. This will keep all of that dust from heading toward the locking mechanism like it’s a vacuum.
The best way to lube up the lock is to completely remove it and get that lube inside and around all of the moving parts before you put it back. If you observe rust, go at it with a long wire brush first, blow it out, then lubricate it.
Frozen Doors and Other Locking Mechanisms
You’d be surprised how many people fail to realize the sliding glass door has a second locking mechanism. Always check for that when you can’t open the door. It could be something as simple as a small, metal, or wood bar sitting on the track.
These bars are deadbolts of sliding glass doors and serve as a good backup device for securing the door. The other possibility tends to rear its ugly head in the winter. You rarely have to worry about it if you live in the south. Read more about sliding glass door locks.
However, for those that live up north or are moving up north, sliding glass doors will sometime freeze in their frames, sticking in place due to ice crusting up in any of the places where moisture develops.
If the door is not completely sealed, condensation forms along the edges.
Overnight, that condensation, created by warm interior air meeting cold outside air, freezes solid, securing your door as effectively as any latch.
Don’t force it and certainly don’t heat it up (that may shatter the glass). You simply have to wait until it thaws if it’s too strong for you to muscle it open.
All Things Considered
The vast majority of the cases are simple adjustments to the clasp and shaft of the sliding glass door.
These are very simple locks and, for what it’s worth, you shouldn’t depend on clasp lock alone anyway.
They’re popular because they’re cheap and because they work. Adjust it if necessary and keep it well-maintained and lubricated whether its working or not.
Read more if your sliding glass door is not closing flush.