If you have older wooden double-hung windows that move up and down, or sliders that open by moving left and right, sooner or later you'll likely have issues with the windows sticking and refusing to open and close smoothly. There are lots of reasons for this, and some of them are pretty serious. For example, structural settling of the house may be causing the window framing to pinch the windows; or the window sashes themselves may be bowing due to age. Here, the best solution is to remove the entire window, reframe the opening, and install an entirely new window.
Fortunately, this serious fix is usually unnecessary. Windows that refuse to slide in their tracks can often be remedied with very simple solutions.
Clean the Window Tracks
Simple dirt and grime can increase the friction and cause windows to bind in their tracks. Vacuum the tracks to remove all dust and dirt, then wipe them clean with a clean cloth moistened with furniture wax (for wood windows) or a household cleaner (for vinyl-track windows). This simple step alone may restore your windows to efficient operation.
Also, inspect the window tracks for dried paint. Windows tracks are not meant to be painted, but they often are, and if the previous paint job was sloppy, it may have left paint drips in the wooden tracks. And older paint may crack and peel, increasing the friction in the tracks. In this case, scraping away loose paint and lightly sanding the window tracks may loosen things up enough to allow the window to move freely. If you choose to paint window tracks, make sure you first scrape away the old paint, sand thoroughly, and apply a very thin coat of paint.
It's even possible that wooden windows have been painted shut inside their tracks, in which case the windows won't budge at all. You usually can break the paint seal between the sash frame and the channel with a sharp utility knife, putty knife, or a tool known as a paint zipper, designed for the purpose.
Lubricate Wooden Window Tracks With Wax
Once you have cleaned the window tracks, you can lubricate the window channels by rubbing the wood surfaces with ordinary wax, such as that from a white candle. A light coat is all it takes. Open and close the window several times to distribute the wax and lubricate the surfaces. Cleaning the tracks and applying the wax once each year will keep your windows operating smoothly.
Lubricate Vinyl Window Tracks With Silicone Lubricant
On vinyl-track windows, the solution to sticking windows is to remove the window sashes, then clean the vinyl tracks and lubricate them with a thin layer of silicone lubricant applied by wiping it on with a clean cloth. Repeat this routine maintenance once each year.
Don't Use Oil
A very common solution—and a very poor one—is lubricating the window tracks with penetrating oil, such as WD-40. Oils will offer only a temporary solution and will soon serve as magnets for dust and grime, making your windows stickier than ever. Never use oil products on either wooden or vinyl windows.
Broken Sash Cords
On older wooden double-hung windows, a system of cords and pulleys attached to metal weights inside the frame openings are used to counterbalance the weight of the window and allow it to move up and down easily. When the lower window is hard to lift upward in its channel—or if the window won't stay in place and slams shut sharply—it may be because the cord-and-weight system is malfunctioning. Most often, this is because the cords that link the pocket weights and the window sash have broken. The solution here is to remove the window and repair the broken sash cords.