A patio door is easy to ignore when it still opens and closes, but that does not always mean it is performing the way it should. Older sliding and French patio doors can gradually develop problems with operation, air leakage, water intrusion, glass seals, locks, rollers, tracks, frames, and overall energy performance. Because these changes often happen slowly, homeowners may adapt to a door that has become increasingly difficult to use without realizing how much the system has deteriorated.