What's actually wrong with your uPVC windows?

Handle needs two hands to turn

This is almost always the gearbox inside the handle wearing out, or the multi point lock mechanism inside the sash needing lubrication rather than replacement. Spray a PTFE based lubricant, not WD40, into the keeps and the gearbox and work the handle through its full travel a few times.

If that does nothing, the handle spindle itself may be worn or snapped inside, in which case the handle unscrews and swaps for a like for like replacement in about ten minutes.

Sash has dropped and catches on the frame

You'll see this as a top corner rubbing on the frame or a window that won't close square any more. It's the hinges, usually called friction stays on a casement window, losing their grip on the weight of the sash over time.

Most stays have an adjustment screw that a fitter can use to lift the sash back into line in a few minutes on site. It only becomes a bigger job if the stay arm itself has cracked or the screws have pulled out of softened uPVC around the fixing points.

Friction stays failed completely

When the stay arm snaps or the sash drops so far it won't shut at all, that's beyond a tweak. A fitter replaces the stay, which is a standard part, and rehangs the sash. It's a straightforward job for someone who does it daily, but not one to attempt with the sash hanging loose and no spare hands.

Cloudy or misted double glazing

A permanent haze or a ring of condensation trapped between the two panes means the seal on the sealed unit has failed and moist air has got in. No amount of cleaning fixes it because the moisture is inside the unit, not on the glass surface.

The glass unit can usually be swapped without replacing the whole window, provided the frame itself is sound. If the frame is old enough that a matching unit is hard to source, or the frame has other faults too, whole window replacement often works out better value.

Lock won't turn or the key sticks

Sticking locks are nearly always dirt and dried grease in the cylinder or the keeps rather than a broken mechanism. Lubricate first. If the key turns but the sash doesn't lock, the keeps have likely moved out of alignment with the sash, which a fitter corrects by adjusting the keep position rather than fitting new hardware.

• DIY: lubricate handles, hinges and locks every six months
• DIY: swap a worn handle for a matching replacement
• Fitter visit: adjust dropped sashes and misaligned keeps
• Fitter visit: replace a snapped friction stay
• Fitter visit or glass swap: misted sealed units
• Replacement: chalky, brittle or discoloured frames
• Replacement: rot, cracked profile or persistent draughts with an old frame

Frames have gone chalky or yellowed

White uPVC that has gone matt, powdery or slightly yellow has suffered ultraviolet degradation of the surface of the profile. It can be cleaned and polished cosmetically for a while, but the degradation is in the material itself and it will return. There's no fix that lasts, and on a south facing elevation it tends to be the first visible sign that the frames are approaching the end of their life.

Trickle vents whistle in the wind

A whistling trickle vent is almost always the little flap inside sitting slightly open or clogged with dust, changing the airflow enough to hum in a gust. Cleaning the vent and making sure the slider is fully open or fully closed, rather than caught halfway, usually stops it. It's a five minute DIY job and not a sign of anything wrong with the window itself.

Condensation on the wall around the frame, not the glass

This one gets confused with a window fault but it's usually a ventilation and cold bridging issue at the reveal rather than the window failing. If it's new since a window was fitted, check the trickle vents are open and extractor fans are working. If it's been building for years around an old frame, the frame may simply be conducting cold into the room faster than a modern profile would, which points toward replacement rather than a spot repair.