A failed window seal occurs when the seal between the panes of glass breaks down, allowing moisture and air to seep in. This can cause several issues, including foggy windows: Moisture trapped between the panes of glass can cause a foggy appearance. This is different from normal condensation, which can be wiped away. Temperature fluctuations: The window might feel colder or warmer than the rest of the room. Mold or staining: You might notice mold or staining along the edge