When a door opens past where it is intended, it puts a strain on the hinges. If this continues, or happens with enough force, the door hinges will be pulled from their position. This is known as a "sprung" door. A sprung door will have a tendency to sag and may require you to lift up on the knob to get it closed. Steps must be taken to re-seat the hinges before the sag becomes so severe that the door refuses to close entirely.
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Remove the Door for Repair
Open the door and wedge shims under it to hold it steady. Remove the screws inserted in the jamb side of the hinges using a drill, beginning at the bottom hinge and working to the top. After removing the door, lay it flat on a pair of saw horses.
Replace Problematic Screws
Examine the screws in the edge of the door. Tighten any loose screws with a screwdriver. Replace stripped screws with screws at least 1/2-inch longer than the originals.
Separate the halves of the hinges by tapping a screwdriver up through the bottom of each hinge with a hammer. This drives the pins up through the top of the hinge. Set the hinge pins aside for reuse.
Drill into the bottom of each screw hole 2 ½ inches deep in the jamb with a 1/8-inch wood bit to provide a pilot hole for the new screws.
Install the hinge plates from the jamb half of the hinges into the mortises in the jamb. Drive one 3-inch wood screw into each hole with a drill. The longer screws will drive through the jamb into the frame behind to anchor the hinges firmly.
Reattaching the Door
Lift the door upright and position the door so that the hinge halves line up. Work the door, by lifting up gently on the handle and pushing toward the jamb, until the hinge halves align completely.
Wedge the shims underneath the door again to hold it up. Drive the hinge pins into the hinges with a hammer, beginning with the top hinge. Lift up slightly on the door to aid stubborn pins in sliding home. Do not hit the pins with too much force, or you will unseat the hinges and be back where you started.
Open and close the door several times to test for proper operation. Correct doors that sag slightly by tightening the top screw in the top hinge to lift the door. Check all hinge screws and tighten any screw that has loosened in the installation process.