Double glazed PVC window. It's just a plain glass window with 1 pane approx 700mm X 800mm. Last week the inside pane broke, It didn't get smashed or anything, It just cracked by itself for no apparent reason. Had a new double glaze unit made and replaced it yesterday then this morning the same thing has happened, the inside pane is cracked. There are 3 big cracks that seem to originate from a point at the edge of the window. Please does anyone know what could possibly have caused this and suggest a way to resolve the problem as cheaply as possible.