The sash has dropped
Every opening window hangs on hinges, and over years of use those hinges wear and the whole sash can drop a millimetre or two on one side. You will usually notice it as a gap at the top of the frame on the hinge side, or the window catching the frame low down on the opposite corner before it will shut.
This is not usually something to force. Pushing a dropped sash shut repeatedly just wears the hinge and the frame corner faster, and can eventually crack the frame or damage the glass unit sitting inside it.
Friction hinges worn or loose
Modern uPVC windows use friction hinge stays, which are designed to hold the window open at any angle and also carry its weight when closing. Over time the friction adjustment loosens, screws work slightly free in the uPVC, or the hinge itself wears. A loose hinge lets the sash tilt or twist very slightly out of true, which is often enough to stop it seating flush in the frame.
Packers, painted or swollen frames
On some installations small plastic packers sit between the hinge and the frame to fine-tune alignment; if one has slipped or was never quite right, the window can bind on one edge. On timber-look composite or older frames, paint building up around the closing edge over repeated repainting can be just enough to stop full contact, and in very damp weather a frame can swell fractionally and do the same thing temporarily.
| Symptom | Likely cause |
|---|---|
| Gap at top on hinge side | Sash has dropped |
| Window feels loose or wobbly when open | Worn or loosened friction hinge |
| Sticks on one edge only, worse in damp weather | Swollen frame or paint build-up |
| Handle turns but window will not lock shut | Cams out of line with keeps |
Cams out of line
The handle drives small rotating cams around the edge of the sash into keeps fixed to the frame. If the sash has moved even slightly, from a dropped hinge or a knock, those cams can miss their keeps, so the handle turns and feels normal but the window simply will not pull shut and lock. This is a very common reason a window seems to close but then rattles or lets a draught through, because it has actually only caught on one point rather than locked fully.
Safe checks before calling us
With the window open, check for visible play in the hinges by gently trying to lift the open sash. Look along the closing edge for obvious paint ridges or swelling you can see or feel. Check the window still lines up squarely with the frame when pushed shut gently, without needing extra force.
- Do not force a sticking window repeatedly, since this usually makes hinge wear or frame damage worse
- Do not sand or plane a uPVC frame; that is a job for the right tools and, sometimes, hinge adjustment rather than material removal
- Do check hinge screws are tight, as a loose screw is sometimes the whole problem
- Do note whether the fault is worse in wet weather, which points toward swelling rather than a mechanical fault
Where to read next
Get a sticking window sorted
Tell us what the window is doing and we will let you know whether it is a quick adjustment or something more, then book you in.