A window that will not lock is easy to ignore for a week, then a month. Meanwhile it is an open invitation on the ground floor, and it leaks air the whole time because the lock is also what squeezes the weatherstripping shut. The fix can be as simple as pushing a sash up half an inch. Sometimes it points to something bigger. Here is how to tell which.
Start with the thirty-second check
On double-hung windows, the most common cause by far is a top sash that has slipped down a little. You cannot always see it from inside. The bottom sash looks closed, you turn the lock, and the cam on one sash misses the keeper on the other because the two rails are not lined up.
Push the upper sash firmly all the way up. Then lower the bottom sash until it sits flat on the sill. Try the lock again. If it turns smoothly now, you are done. Make a habit of checking the top sash whenever a lock feels stiff.
On single-hung windows the top sash is fixed, so skip straight to the bottom one. On sliders, push the moving panel firmly against the side jamb.
Match the symptom to the cause
The lock turns but does not catch anything
The two halves of the lock are not meeting. Besides a dropped sash, check whether a tilt latch on the bottom sash has popped out of its track. If one corner of the sash sits slightly forward, the lock cannot line up. Tilt latches should be flush and fully engaged on both sides.
Also look at the screws holding the lock and the keeper. Loose screws let the hardware shift out of line. Snugging them with a screwdriver is a reasonable fix. Do not overtighten screws in vinyl, because they strip easily.
The lock will not turn at all
Look for something physical in the way. Paint, dried caulk, dead insects, a curtain cord, or grit packed into the lock mechanism can all stop it. Clean around the lock with a dry brush and a vacuum. A light touch of silicone spray on the moving parts can free a stiff cam. Avoid heavy oils, which collect dust and make the problem worse over time.
The sash will not close all the way
If the bottom sash stops a fraction of an inch above the sill, check the track for debris first. Leaves, pebbles and pieces of a broken screen end up in tracks more often than you would think. Vacuum the full length of the sill.
If the track is clean and the sash still will not seat, the window may be out of square. That leads to the bigger causes below.
It locks in winter but not in summer, or the reverse
Seasonal changes in how a window closes usually point to movement in the house rather than a problem with the window itself.
Sliders and casements have their own quirks
On a horizontal slider, the lock usually sits where the moving panel meets the frame or the fixed panel. If it will not catch, the panel may have jumped off its rollers or the bottom track may be packed with grit. Lift the panel slightly and slide it closed again. A panel that sits lower on one end than the other often needs its rollers adjusted, which is a job for the installer on a newer window.
Casement and awning windows use a handle that pulls the sash tight against the frame, and some have locking points along the edge. If the handle will not move, the sash is probably not fully cranked shut. Turn the crank until the sash touches the frame all the way around, then try the handle. If the crank spins without moving the sash, the operator is stripped and needs replacing.
Austin’s summer heat also plays a part. Vinyl expands slightly on a sunbaked west wall, and a window that locks easily at 8 in the morning can feel tight at 5 in the afternoon. A small seasonal change is normal. A window that cannot lock at all in the heat is not.
When the house is the problem
Parts of the Austin area sit on expansive clay soil. It swells when wet and shrinks during long dry stretches, and foundations move with it. As a slab shifts, wall openings go slightly out of square, and a window that was perfectly aligned at installation starts to bind or miss its lock. Telltale signs elsewhere in the house include:
- diagonal cracks in drywall running from the corners of windows and doors
- interior doors that stick or swing open on their own
- gaps between trim and wall, or between brick and window frame
- several windows on the same side of the house developing the same problem
Forcing a sash into position against a twisted frame can crack the vinyl or break the lock. If you see these signs, have a foundation professional look at the house before you replace hardware or windows. Sometimes the movement reverses after a wet season. Sometimes it needs repair.
When the window is the problem
Older wood windows absorb water through failing paint and caulk. The wood swells, the sash sticks, and once the frame warps the lock may never line up again. Single-pane aluminum windows from the 1970s and 1980s have their own issues: thin frames that bend, lock hardware that wears out, and replacement parts that are hard to find.
With windows like these, repairing one lock often buys time but does not solve much. If several windows on the house have the same trouble, it may be time to look at replacement windows instead.
Newer windows: call before you take anything apart
If the windows were installed in the last several years and none of the simple checks above help, contact the company that installed them. Each manufacturer designs its own locks, keepers and tilt latches, and warranty terms frequently include them. The balance system that holds the sash up is under spring tension and should not be adjusted by a homeowner. Pulling a sash out of its track to look at the lock is the kind of DIY repair that can turn a warranty service call into a paid one.
Have the window’s serial number or label information ready when you call. It tells the installer which hardware to bring.
Keeping the house secure in the meantime
While you wait for a fix, secure the window another way. A cut dowel or a length of wood laid in the track of a slider or above the bottom sash of a double-hung keeps it from opening. Clamp-on sash stops from a hardware store work too. Keep in mind that a blocked window cannot serve as a fire exit, so do not block a bedroom window overnight unless there is another way out of the room.
If your locks keep giving you trouble, The Window Source of Austin can take a look. Call (512) 524-9455 to schedule a free in-home estimate, or send us a message.