Window won't stay open and slides shut — Elche, Valencian Community

A window that slowly slides shut on its own—or slams down unexpectedly—has a failed balance mechanism. In modern single- and double-hung windows, a pair of spring-loaded block-and-tackle or coil-spring balances hidden in the side jambs counterweigh the sash. When the spring breaks, the cord snaps, or the balance shoe wears out, the sash has nothing holding it up. Older windows use a sash-cord-and-weight system where a cotton or nylon rope runs over a pulley to a cast-iron counterweight inside the wall cavity; when the cord frays and breaks, the weight drops and the sash falls. A handyman can replace balance springs or restring sash cords typically in 30–60 minutes per window, restoring smooth, stay-put operation without replacing the entire window.