Short Answer
Look for staining, peeling paint, damaged trim, soft wood, condensation, drafts, water intrusion, and deterioration around the opening.
Detailed Explanation
Window leaks can show several signs: water stains on the wall or ceiling around the window, peeling paint or bubbling wallpaper near the window, soft or rotted wood in the sill or frame, condensation between glass panes (indicating failed seals), drafts that can be felt around the window edges, visible water entering during rain, and deteriorated or missing caulk and weatherstripping. Some of these signs indicate the window itself is failing (condensation between panes, rotted frame), while others may indicate a flashing or installation problem (water stains, peeling paint) rather than a window defect. A proper diagnosis evaluates both the window and the surrounding installation.
Why It Matters
Window leak symptoms can indicate either window failure or installation/flashing problems. Correct diagnosis determines whether the window needs replacement or the flashing needs repair.
When Repair Makes Sense
Leaks are caused by failed sealant, weatherstripping, or flashing that can be repaired without replacing the window.
When Replacement Makes Sense
The window frame is rotted, seals have failed, or the window itself is structurally compromised.