uPVC window won't close or lock properly? How to find the fault and fix it

A uPVC window that suddenly needs a shove to shut, or a handle that will not go all the way down, is one of the most common calls we take. The good news: in most cases nothing is broken yet, the sash has simply dropped a few millimetres. The checks below find the fault in a few minutes, and two of the fixes need nothing more than a screwdriver.

The short answer

Open the window and watch the bottom edge of the opening sash as you close it. If it scrapes or catches the frame, the hinges have worn and the sash has dropped. If it closes cleanly but the handle will not lock, the locking cams are missing their keeps. If the handle feels loose or spins, the gearbox is failing. Each has a different fix, below.

Before you start

• Close the window gently and never force the handle. A forced handle is how a cheap adjustment becomes a broken gearbox.
• Have a cross-head screwdriver, a 4mm hex key, a torch and a can of light oil or silicone spray to hand.
• Work from inside. If the window is above the ground floor, do not lean out to reach the hinges.

Step 1: find where it catches

Close the window slowly and look at the gap round the edge with a torch. Run a sheet of paper round the closed sash, too.

• Rubs at the bottom on the handle side: the sash has dropped on its hinges. Go to Step 2.
• Closes freely but the handle stops halfway: the cams are hitting the keeps. Go to Step 3.
• Handle loose, stiff or turns without moving anything: go to Step 4.
• Closes and locks but you can feel a draught: the gasket is tired. Go to Step 5.

Step 2: tighten and clean the friction hinges

Most uPVC casements open on friction stays, the two metal arms you can see top and bottom when the window is open. Over time the screws loosen and the slider wears.

1. Open the window fully and look at both hinges. Tighten any loose screws, but do not overtighten into the plastic.
2. Clean grit out of the track with a dry brush, then apply a few drops of light oil to the pivots and slider. Open and close it ten times and wipe off any excess.
3. If the hinge arm is bent, cracked or flops loosely, it needs replacing. Hinges come in specific lengths and weights, so count the length in millimetres and note the stack height before ordering.

A sash that has dropped because of a worn hinge comes back into line as soon as the new hinge is fitted.

Step 3: adjust the locking cams

Look along the edge of the sash on the handle side. You will see small round cams, often mushroom-shaped, that slide into keeps on the frame when the handle turns.

1. With the window open, turn the handle to the locked position and watch the cams move.
2. Many cams are eccentric: they have a hex hole or a slot in the middle. Turn a quarter turn with a 4mm key to pull the sash in tighter or let it out.
3. Adjust all cams by the same amount, test, and repeat. Small turns, one at a time.

If the cams line up but still hit the keeps, the keep screws may have loosened and the keep has slipped. Loosen, slide back into line and tighten.

Step 4: handle and gearbox problems

Remove the handle by turning the cover plate at its base and undoing the two screws. Slide it off.

• The handle is cracked or the spindle has snapped: fit a new handle with the same spindle length. A quick DIY job.
• You can turn the spindle hole with a screwdriver and the mechanism moves freely: the handle was the problem.
• The spindle hole will not turn, or turns without moving the cams: the gearbox inside the sash has failed. It has to be cut out and replaced, and with the window stuck shut it is a job for a glazier.

Step 5: tired gaskets and draughts

The rubber gaskets in the frame shrink and harden over the years. Clean them with warm soapy water and wipe on a little silicone. If they are cracked or have shrunk back from the corners, they can be replaced: we re-run new gasket of the right profile in one continuous length round the sash.

Quick fault finder

Symptom	Likely cause	DIY?
Scrapes frame when closing	Worn or loose friction hinges	Tighten yes, replace usually
Handle stops halfway	Cams not meeting keeps	Yes, small adjustments
Handle floppy or turns without locking	Failed gearbox	No, call a glazier
Handle snapped, mechanism fine	Broken handle	Yes
Shuts and locks but draughty	Worn gasket	Clean yes, replace usually
Mist between the panes	Failed sealed unit	No, see our blown unit tests

When to call us

Call a glazier if the window is stuck open or stuck shut, the gearbox has failed, a hinge has bent, or the window is above the ground floor. Our uPVC window repair service carries common hinges, gearboxes and handles on the van, so most repairs are done on the first visit. Send a photo on WhatsApp of the hinge and the handle with the window open, and we will tell you which part it needs. For a window that will not lock at night, ring 07915 903485 at any hour.

Doors give the same trouble in a bigger way. If it is your back door that is sticking, read how to adjust a uPVC door that has dropped.