A broken window lock is rarely a mystery once you know what kind of window it sits on. The lock on a double hung sash, the latch on a horizontal slider, the operator and lever on a casement, the multipoint hardware on an impact-rated unit, and the small keyed locks sold as add-ons for any of them are five different mechanisms, and each one fails at a predictable point for a predictable reason. Identifying the window type first, and then reading the failure against what that type is known for, gets to the right repair faster than any general list of window lock problems, and it also sorts out the question that comes up on nearly every one of these calls: whether this is a locksmith job, a window company job, or a five-minute adjustment the owner can make.
Single and double hung windows: the sash lock
A hung window has one or two sashes that slide vertically. The lock lives on the meeting rail, the horizontal bar where the top of the lower sash meets the bottom of the upper sash. The most common form is a cam lock, sometimes called a crescent or sweep lock: a lever on the lower sash swings a curved cam into a keeper mounted on the upper sash, pulling the two rails tight together. Better windows use a spring-loaded sash lock that snaps closed when the sash is fully raised, or two locks on wider sashes.
The most frequent failure is not in the lock at all. The lower sash is not fully up, so the cam swings past the keeper without engaging, or catches only its edge and pops free under pressure. On a wood window that has swelled, or a vinyl window whose sash balance has weakened, the sash stops a quarter inch short of the top and the lock never reaches. Push the sash all the way up with both hands and try the lock again before assuming anything is broken. If it locks with the sash held up and unlocks itself when the sash is released, the balance, the spring or block-and-tackle inside the jamb that holds the sash weight, has failed, and that is a window repair rather than a lock repair.
The second failure is stripped mounting screws. Sash locks on vinyl and aluminum windows are screwed into thin walls, and years of levering the cam closed against a slightly misaligned keeper pull the screws loose. The lock rocks on the rail, the cam no longer reaches full engagement, and the whole thing eventually lifts off. On vinyl, the fix is longer screws into the reinforcement inside the sash or a small backing plate, not the same screws driven back into the enlarged holes.
The third is a broken cam or keeper. Zinc cams crack at the pivot, and plastic keepers on budget windows shear their lip. Either is a replacement of the piece, which comes in a handful of standard hole spacings. Match the spacing, the handing, and the cam height, because a keeper set too high or too low is the same as no keeper.
Tilt-in double hung windows add one more piece: the tilt latches at the top corners of the lower sash. When one breaks, the sash can tilt inward on its own or sit crooked in the track, and the sash lock will not line up with its keeper because the sash is not square in the frame. Replace the tilt latch first and the lock problem usually disappears.
Horizontal sliding windows: the latch
A sliding window has one fixed panel and one that rolls sideways on a track. The lock is a latch on the sliding panel’s stile, the vertical edge that meets the frame, engaging a keeper on the frame. Most are a spring-loaded hook or a cam operated by a small lever, and on cheaper windows the lever, the hook, and the housing are all plastic.
The signature failure of a slider latch is a lever that moves but does nothing. Inside, the plastic hook has snapped off or the tab that links the lever to the hook has sheared. It is the same fault that takes out the latch on a patio door, in a smaller housing, and the page on a sliding glass door lock that is broken describes the identical mechanism at a larger scale. On a window, the latch is a replaceable unit held by two screws, and the main challenge is finding the matching part, since slider latches are not standardized across manufacturers.
The second failure is alignment, and it comes from the rollers. The sliding panel rides on small wheels at the bottom, and when they wear, the panel drops. The latch on the panel now sits lower than the keeper on the frame, so the hook cannot reach, or catches only the top edge. A panel that has become hard to slide, or that scrapes, has worn rollers, and the latch problem is a symptom. Roller replacement is a window job, and until it is done, any latch fix is temporary. Adjusting the keeper downward buys time but should not be the only repair.
The third is the keeper itself, a small metal or plastic piece that pulls loose from the frame. On aluminum sliders the keeper screws strip out the same way sash lock screws do on vinyl. On many sliders the keeper is a stamped tab that has bent from years of the hook slamming into it, and bending it back or replacing it restores the latch.
Sliders also have a specific weakness the latch does not address: the panel can be lifted up and out of its track from outside if the anti-lift blocks are missing. A latch that works perfectly does not secure a slider that can be lifted. Check that the track has anti-lift screws or blocks at the top, and consider a pin lock or a bar in the track as a second lock, which is also the fastest way to secure a slider whose latch is broken until the part arrives.
Casement windows: the operator and the locking lever
A casement window hinges at the side and swings outward, opened by a crank operator at the sill and locked by one or more levers on the lock stile. On a single-point casement, one lever pulls a keeper on the sash tight against the frame. On a multipoint casement, common on windows taller than about three feet, the lever moves a tie bar that engages two or more keepers along the stile at once.
Casement failures split between the operator and the lock, and they are often confused because both stop the window from locking. The operator has a worm gear and a pivoting arm. When the gear strips, the crank spins and the sash does not move, or the sash moves for part of the travel and then the crank slips. A stripped operator cannot pull the sash fully closed, so the sash sits a fraction open, the keeper on the sash does not reach the lever’s hook, and the lock cannot engage. The owner sees a lock that will not close and the actual fault is the operator. The test is to push the sash closed by hand from inside while someone works the lever. If it locks with the sash pushed, the operator is the problem. Operators are replaced as a unit, matched by the arm type and the handing, and this is a window hardware job that a locksmith who handles window hardware can do, as can a window company.
Lock lever failures are their own category. The lever pivots on a pin that wears, the hook on the lever wears until it slips off the keeper, or on a multipoint window the tie bar disconnects from one of its keepers so the lever moves freely but only some of the points engage. A lever that moves through its full travel with no resistance at all is usually a disconnected tie bar or a broken hook. A lever that stops halfway has a keeper out of position, often because the sash has sagged on its hinges. Casement hinges carry the sash on a pivot arm, and when the arm’s track fills with debris or the pivot wears, the sash drops at the lock side, and every keeper is now a fraction too low.
Casement hardware is more expensive and more manufacturer-specific than sash or slider hardware. The window brand and the year matter, and a photo of the operator and lock with a tape measure across them is the first thing to send to whoever is sourcing the part.
Impact-rated windows: multipoint hardware under load
Impact-rated windows, standard on newer construction and replacements in South Florida, are built to meet large-missile and cyclic pressure testing. The glass is laminated, the frames are heavier, and the locks are part of the tested assembly. Single hung impact windows typically have two sash locks on the meeting rail, sliders have reinforced latches with metal hooks, and casements have multipoint locks with steel tie bars. The hardware is under real load every time the wind blows, because the sash is holding pressure against the frame.
What breaks on impact windows is the same list as above, with two differences. The first is that the parts are heavier and the failures are less often the part and more often the fasteners and the alignment. A sash lock on an impact single hung window that will not engage is more likely to have a sash that is not square in the frame, from a balance failure or from the frame itself racking after a storm, than a broken cam. A slider latch that will not catch usually has a panel that dropped on its rollers under the weight of laminated glass, which is heavier than the rollers on older windows were built for.
The second is that the replacement hardware has to match. The window’s rating is based on the assembly as tested, and swapping the two meeting rail locks for a single generic cam lock, or fitting a plastic slider latch in place of the metal one, means the window no longer has the hardware it was approved with. An owner who wants the window to keep its rating for insurance and for the next inspection replaces broken parts with the manufacturer’s parts or an approved equivalent. That usually means the window company or a hardware supplier that carries impact-rated components, and it means keeping the paperwork.
Impact windows also come with a specific complaint after a storm: locks that worked before the wind and do not after it. The sash and frame may have shifted under pressure and not returned to square. Before replacing any hardware, the window itself needs to be checked for a racked frame, a sash that has come off its balance, or a slider panel that jumped its track. Hardware fitted to a window that has moved will fail again.
Keyed window locks: the add-on that gets lost
Keyed window locks are sold to add a second lock to any of the window types above, and they take three forms. A keyed sash lock replaces the standard cam lock on a hung window with one that needs a key to unlock. A keyed slider lock clamps onto the track or the frame with a set screw or a thumbscrew and locks with a small cylinder. A pin lock drives a steel pin through the sash into the frame, with a keyed or push-button head.
The way these fail is almost always the key. They use small wafer or pin cylinders with keys that are not part of any house key system, and the keys are lost, left in a drawer, or the window is sold with the house and the keys are not. A keyed window lock without its key is a locksmith job in the same sense as a lost cabinet key, and the page on a cabinet lock with a lost key describes the same small cylinders and the same options: pick it and open it once, cut a key by code or by impressioning, or replace the lock and keep the keys somewhere findable. Most keyed window locks share a small number of keyways and a locksmith can usually open and key them on the spot.
Mechanical failures on keyed window locks are usually the clamp. A slider lock that has been tightened and loosened hundreds of times strips its thumbscrew and slides on the track. A pin lock’s pin bends if the sash is forced with the pin in. These are replaced, not repaired.
The larger issue with keyed window locks is safety, not security. A bedroom window that needs a key to open is a window that cannot be used to get out in a fire, and a keyed lock on any window that serves as an emergency exit is a hazard that fire codes do not permit in sleeping rooms. A locksmith asked to install or replace keyed window locks will ask which rooms they are for, and the right answer for a bedroom is a non-keyed secondary lock or a pin lock with a push-button release, not a lock that depends on finding a key in the dark.
The five-minute checks that apply to every type
Before any hardware is replaced, three things should be confirmed on any window. The sash or panel is fully closed, all the way to its stop, with no weatherstripping folded under it and no debris in the track. The sash sits square in the frame, with the same gap at the top and bottom, or left and right, on both sides. And the keeper is where the lock expects it, which is checked by closing the window and looking at where the lock’s hook or cam lands relative to the keeper’s opening. If all three are right and the lock still fails, the part is broken. If any of them is wrong, the lock is probably fine and the window has moved.
What not to do with a window that will not lock
Do not force a lever that has stopped. The zinc and plastic parts in window locks break under the hand pressure that a stuck door lock might survive, and a lever forced past a jammed keeper becomes a broken lever with a jammed keeper behind it. Do not screw a broken sash lock back into stripped holes with the same screws; it will pull out again in weeks. Do not glue or epoxy any piece of a window lock, which is the surest way to make the eventual replacement harder. Do not replace impact window hardware with generic parts and expect the window to keep its rating. And do not leave a window unlocked because the lock is broken. A screw driven through the sash into the frame from inside, a pin lock, or a dowel in the track secures any window type overnight until the correct part is fitted.
Which trade handles which failure
Sash locks, keepers, slider latches, casement lock levers, and keyed window locks are hardware, and a locksmith who works on window hardware replaces and adjusts them. Balances, rollers, casement operators, hinges, and anything involving the sash or frame itself belongs to a window company or a glazier, and on impact-rated windows the window company is the right first call for anything that affects the tested assembly. On a lock that fails because the sash has moved, the honest sequence is window first, lock second, because a lock fitted to a window that has not been squared will fail again within the year.
Pro Locksmith replaces and adjusts window locks, latches, and keyed window hardware for homes and businesses across Broward County, opens and keys keyed window locks with lost keys, and secures windows with broken hardware on an emergency basis, with 24-Hour Emergency service when an unlockable window cannot wait for morning. Before calling (954) 406-8266, identify the window type from the sections above and take a photo of the broken hardware, since the type of window decides the part, and the part decides the visit.