Key Turns But Bolt Will Not Throw Only When Door Is Closed
Why this matters
A deadbolt that throws freely with the door open but binds or refuses to extend when the door is closed is one of the most misdiagnosed service calls in residential locksmithing. The reflex is to blame the cylinder or replace the lock, but the cylinder is almost never at fault: the key turns, the tailpiece rotates, the bolt mechanism functions. The constraint appears only when the door is in the frame, which points to a geometry problem between the bolt and the strike, not a lock-internal problem. Throwing the bolt against a misaligned strike forces the bolt to plow into the strike lip or the wood behind it, and a customer who muscles it daily will eventually shear the bolt or crack the lock body. Correctly isolating strike misalignment from door sag, seasonal swell, and weatherstrip compression saves you from replacing a perfectly good lock and from a callback when the real cause reasserts itself.
Symptom presentation
The customer reports the key turns part way and stops, or turns fully but the bolt only extends a fraction before it catches. With the door swung open, the same key throws the bolt smoothly its full travel into open air. Listen for the difference: a clean throw produces one continuous slide; a binding throw produces a gritty drag, a hard stop, or a metallic scrape. Ask whether the problem is new, seasonal, or progressive. Seasonal onset (works in summer, binds in winter, or the reverse) signals door or frame movement with humidity. Sudden onset after a slammed door, a new closer, or fresh weatherstrip points to a discrete mechanical change. Gradual worsening over months points to hinge wear or settling.
Quick checks
Run these before opening anything. With the door open, throw the bolt fully and confirm free travel; this isolates the cylinder and bolt mechanism as healthy. Close the door and look at the bolt-to-strike relationship through the gap: the bolt should align centered with the strike hole. Coat the bolt face with lipstick, a grease pencil, or layout dye, throw it against the closed strike, and inspect the transfer mark on the strike plate. A mark high, low, or to one side tells you the exact direction of misalignment in one test. Check the door gap (reveal) along the latch edge top to bottom; an uneven reveal means the door is no longer square in the opening.
Isolation tree
Start from the lipstick transfer mark.
Branch 1, mark centered but bolt still binds: the strike hole or bolt pocket in the jamb is too shallow or partially obstructed. Look for paint buildup, a swollen wood pocket, debris, or a strike plate whose box does not align with the drilled mortise. Probe the pocket depth with the bolt length.
Branch 2, mark high or low on the strike: vertical misalignment. Test for door sag by lifting the latch edge with a pry bar at the bottom while a helper throws the bolt; if it suddenly throws, the top hinge is loose or worn and the door has dropped. Check hinge screws, especially the top hinge top screw into the stud. If lifting does not help and the reveal is even, the strike is simply mounted too high or low.
Branch 3, mark to the latch side (bolt hits the strike lip before entering): the door is not pulling in far enough, or the strike sits proud. Cause candidates: compressed or new weatherstrip holding the door off the stop, a swollen door slab, a closer or hinge spring not seating the door, or a strike mortised too shallow so its lip stands out.
Branch 4, mark changes with weather: confirm seasonal swell. Measure the reveal in the failing season versus a known-good photo or the opposite edge. Swelling that closes the gap also shifts bolt position.
Confirming diagnosis
Confirm before cutting metal or wood. For sag, snug the top hinge screws (replace short screws with 3 inch screws into the stud) and re-run the lipstick test; a centered mark confirms the hinge was the cause. For shallow pocket, chisel or drill the bolt pocket to full bolt depth plus clearance and confirm full manual throw with the door closed. For strike misalignment, mark the new strike position from the transfer test, then dry-fit by throwing the bolt before final fastening. For swell, confirm by reproducing only in the affected season or by inducing the gap change with a clamp; treat the door edge, do not chase the strike to a position that fails in the dry season.
Never enlarge a strike hole or grind a bolt to force engagement without first correcting alignment. A bolt that only catches by a sliver of strike metal has dramatically reduced holding strength and defeats the security rating of the lock. ANSI/BHMA A156.5 grade deadbolts assume full bolt projection into a properly sized strike; partial throw is a security failure, not a fix.
Remediation
For a sagged door, tighten or replace hinge screws and re-shim if needed, then verify the bolt throws full travel closed. For a shallow or obstructed pocket, clear paint and debris, deepen the pocket to full bolt length, and reinstall a reinforced strike box. For a mispositioned strike, relocate per the transfer mark; for minor errors, file the strike hole in the direction of misalignment and refinish exposed edges, but only when the bolt still achieves near-full projection. For weatherstrip holding the door open, replace overbuilt stripping with a profile that lets the door seat, or adjust the stop. For seasonal swell, plane or sand the binding door edge and seal the bare wood so it does not re-absorb moisture. After any fix, throw the bolt closed twenty times and confirm consistent, full, drag-free travel.
References
- ANSI/BHMA A156.5, American National Standard for Cylinders and Input Devices for Locks (deadbolt full-projection and strike requirements)
- ANSI/BHMA A156.36, American National Standard for Auxiliary Locks (deadbolt grade performance)
- Door and Hardware Institute (DHI), Installation of Builders Hardware and Finish Hardware guidance on strike alignment and door reveal
- Schlage B-Series Deadbolt Installation Instructions (manufacturer strike-positioning and bolt-throw verification)