Drafts in uPVC windows almost always come down to three things: gasket compression, hardware tension, or installation gaps. Here is how to diagnose each.
If your window feels draughty, pull a sheet of paper between the sash and frame and try to remove it after closing the handle. If it comes out without resistance, the gasket has lost compression — replace it with a matching EPDM profile.
Hardware tension can be adjusted via the eccentric rollers on the sash edge. Rotate them with an Allen key to bring the sash tighter against the frame.
Installation gaps are best found with a smoke pencil. If you find them, re-foam the perimeter and re-cover with vapour-tight tape — the membrane is what stops the wind, not the trim.
