A window that is stuck shut, slides with difficulty, or will not stay open is frustrating and can be a safety issue — windows are emergency exit routes in bedrooms. The cause is usually paint, broken balances, or swelling, all of which have straightforward fixes.

How to Fix a Window That Won’t Open or Close

Painted Shut

The most common reason a double-hung window will not open.

Score the paint seal between the sash and the frame with a utility knife, cutting along both sides and the bottom of the sash
Insert a stiff putty knife into the seam and tap gently with a hammer to break the paint bond
Work around the entire perimeter of the sash
For stubborn windows, use a special paint zipper tool (a serrated blade designed for this purpose, about $5)
Once freed, sand the paint buildup from the sash edges and the channels where the sash slides
Apply a thin coat of paste wax or spray silicone lubricant to the channels

Do not use a pry bar or screwdriver to force the sash — you will damage the frame.

Swollen Wood

Wood sashes absorb moisture and swell, especially in humid seasons. If the window opened fine last winter but sticks in summer:

Wait for dry weather if possible — the sash may free itself
If you need to open it now, use the utility knife and putty knife method above
Once open, sand the contact points lightly with 80-grit sandpaper
Seal all exposed wood surfaces with primer and paint to reduce future moisture absorption
Run a dehumidifier to reduce indoor humidity

Broken Window Balance (Sash Won’t Stay Open)

Double-hung windows use a balance mechanism to counterweight the sash so it stays where you position it. Older windows use sash weights on ropes. Newer windows use spring balances or block-and-tackle balances in the frame channels.

Spring Balance

Tilt the sash inward (most modern windows tilt for cleaning)
Disconnect the balance from the sash — it hooks or clips into a slot on the sash side
Note the balance model number stamped on it
Order a replacement from a window parts supplier or take it to the hardware store
Connect the new balance and reset the sash in the track

Sash Cord (Older Windows)

Remove the interior stop molding (the trim piece holding the sash in the frame)
Swing the sash out and disconnect the cord from the sash
The sash weight is inside the wall cavity — access it through a small panel in the side of the frame (called the access plate)
Feed new sash cord over the pulley at the top of the frame
Attach the cord to the weight and the sash
Replace the stop molding

This is a more involved repair but straightforward with patience. Replacement sash cord is available at hardware stores for a few dollars.

Channel Cleaning and Lubrication

For windows that slide but with difficulty:

Open the window fully
Clean the channels (the grooves the sash slides in) with a stiff brush and vacuum
Sand any rough spots or paint buildup
Apply dry silicone spray or paste wax to both channels
Slide the window up and down several times to distribute the lubricant

Do not use oil-based lubricants — they attract dust and create a gummy residue over time.

Vinyl Window Adjustments

Vinyl windows can warp slightly, especially in direct sunlight. If a vinyl window sticks:

Clean the tracks
Check for debris in the track or frame
Verify the lock mechanism is fully disengaged before trying to open
If the frame is warped, contact the manufacturer about warranty replacement — vinyl warping is often a defect covered by warranty

When to Replace

Replace the window when:

The frame is rotted and cannot hold hardware
Glass seals have failed (foggy double-pane)
The window cannot be made to operate safely
Weatherstripping and sealing cannot resolve draft issues
Energy efficiency upgrades justify the investment

Most stuck or stiff windows are a maintenance issue that costs nothing or a few dollars to fix.