Short answer: A deadbolt that suddenly resists, sticks halfway, or refuses to line up with its hole is rarely a broken lock. Most of the time it is one of a handful of ordinary problems, and knowing which one you have tells you whether it is a five-minute adjustment or a hardware swap.
A deadbolt that suddenly resists, sticks halfway, or refuses to line up with its hole is rarely a broken lock. Most of the time it is one of a handful of ordinary problems, and knowing which one you have tells you whether it is a five-minute adjustment or a hardware swap.
By far the most frequent cause is a misaligned strike: the bolt no longer lines up with the hole in the frame, so it drags on the metal plate or the wood behind it. This is classic in older Boston housing stock, where a triple-decker or a century-old brownstone settles and shifts with the seasons, and it is worst in humid August when doors swell and in deep winter when framing contracts. The tell is a bolt that throws freely with the door open but binds when the door is shut. Next most common is a dry or dirty cylinder that makes the key hard to turn in any position, then a loose or worn thumbturn, and finally a genuinely failing mechanism where the internal tailpiece is stripped. Ice and packed grit are a distinctly local seasonal cause worth ruling out before you assume the lock itself is bad.
The fastest home test isolates alignment from mechanism: open the door fully and throw the bolt into open air. If it slides smoothly, the lock is fine and your problem is the strike or the door position, not the cylinder. Now close the door and watch where the bolt lands relative to the strike hole; a smudge of lipstick or chalk on the bolt tip will leave a mark showing whether it is hitting high, low, or to one side. A locksmith does the same reasoning but goes further, checking hinge screws that may have loosened and let the door sag, confirming the strike box is deep enough, and testing the key in the cylinder alone off the door. For a sticky-but-working cylinder, the correct fix is a dry lubricant like graphite or PTFE, never a thick oil, because oil collects grime and turns a minor drag into a seized lock within a year.
Alignment problems are usually a repair, not a replacement. Tightening or replacing long hinge screws to lift a sagging door, filing or repositioning the strike plate, or deepening the mortise behind it will fix the great majority of 'won't latch' complaints, and that kind of adjustment often falls in the modest end of a service call rather than the cost of new hardware. Replacement makes sense when the cylinder is worn enough that the key turns loosely or catches internally, when the thumbturn spins without throwing the bolt, or when the deadbolt is old, builder-grade, and you want a higher security grade anyway. A trustworthy locksmith will show you the failed part and explain why an adjustment won't hold before recommending you buy a new lock; if the first and only answer offered is 'replace everything,' get a second opinion.
By far the most frequent cause is a misaligned strike: the bolt no longer lines up with the hole in the frame, so it drags on the metal plate or the wood behind it. This is classic in older Boston housing stock, where a triple-decker or a century-old brownstone settles and shifts with the seasons, and it is worst in humid August when doors swell and in deep winter when framing contracts. The tell is a bolt that throws freely with the door open but binds when the door is shut. Next most common is a dry or dirty cylinder that makes the key hard to turn in any position, then a loose or worn thumbturn, and finally a genuinely failing mechanism where the internal tailpiece is stripped. Ice and packed grit are a distinctly local seasonal cause worth ruling out before you assume the lock itself is bad.
The fastest home test isolates alignment from mechanism: open the door fully and throw the bolt into open air. If it slides smoothly, the lock is fine and your problem is the strike or the door position, not the cylinder. Now close the door and watch where the bolt lands relative to the strike hole; a smudge of lipstick or chalk on the bolt tip will leave a mark showing whether it is hitting high, low, or to one side. A locksmith does the same reasoning but goes further, checking hinge screws that may have loosened and let the door sag, confirming the strike box is deep enough, and testing the key in the cylinder alone off the door. For a sticky-but-working cylinder, the correct fix is a dry lubricant like graphite or PTFE, never a thick oil, because oil collects grime and turns a minor drag into a seized lock within a year.
Alignment problems are usually a repair, not a replacement. Tightening or replacing long hinge screws to lift a sagging door, filing or repositioning the strike plate, or deepening the mortise behind it will fix the great majority of 'won't latch' complaints, and that kind of adjustment often falls in the modest end of a service call rather than the cost of new hardware. Replacement makes sense when the cylinder is worn enough that the key turns loosely or catches internally, when the thumbturn spins without throwing the bolt, or when the deadbolt is old, builder-grade, and you want a higher security grade anyway. A trustworthy locksmith will show you the failed part and explain why an adjustment won't hold before recommending you buy a new lock; if the first and only answer offered is 'replace everything,' get a second opinion.
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