Properly installed kitchen cabinets should stay mounted to the wall securely for a long time. Occasionally from continual use, overloading of cabinets with heavy items or pulling and slamming cabinet doors, they can start to come loose and need reattaching to the wall. Fixing your kitchen wall cabinets and making sure they are securely attached to the wall again is a fairly easy process.
Check levelness on horizontal and vertical sides of the cabinet by placing a level on each outer edge.
Fix misalignment or unevenness of the cabinet by loosening the screws at the back of the cabinet with a screwdriver. Squeeze in shims or small scraps of wood around the back and side of cabinet in voided areas to square or level it. Use a level several times until it shows shimming has squared the cabinet.
Check for studs in the wall to drill screws into. Improper initial installation of wall cabinets may have contributed to cabinets sagging or coming loose and finding a stud for the screws is imperative. Original screw holes may have been placed poorly or got larger and drilling new screw holes is advised. Longer screws may hold the cabinet more securely along with adding extra screws. Butterfly bolts or a drywall anchor can be used in place of a screw if a stud is not available on the wall.
Correct cabinet doors that do not line up with each other across the same line vertically by adjusting the hinge. Loosen the screw to the hinge, adjust the door up or down until the cabinet doors are even. Tighten the hinge screws.
Fix the gap between cabinet doors that is more than norma--one-eighth inch or less. Loosen the screw on the hinge and slide the spacer (if applicable for your hinge type) or slide the door inward until the correct gap is achieved between the doors. Tighten the hinge screw and repeat for the bottom hinge if necessary.
Support the upper wall cabinet before you start if you do not have a second person to hold it while you work. Use 2-by-4-inch wood pieces for supports that are braced on the lower cabinet, counter or adjacent wall, if necessary. Cabinet manufacturers offer warranties on the cabinets themselves. Defects from production may be possible, but rare. If they were installed correctly and still have maintenance problems, check with your cabinet manufacturer for warranty stipulations.