(Difficult to Open Example):
I couldn’t open the window, it was stuck, jammed and seized shut. The window handle moved, but the window just won’t open?
When you close the window, the gearbox (which is attached to the handle) pushes shootbolts (espag or espagnolette) and roller cams (mushrooms) out to lock the window in the outermost corners. Parts of the gearbox can break, or the shootbolts can seize preventing the window from opening….
More detailed information can be found on this page: How to Open a Jammed, Stuck, or Seized uPVC Window: (Opens in a new tab)