If you have to lift the door, shove it, or pull it towards you before the deadbolt will turn, the lock is almost certainly innocent. Something else moved, and replacing the lock will not put it back.
What a door is actually doing all year
A door and its frame are wood, and wood responds to humidity. Through a York Region summer the frame takes on moisture and swells. Through January it dries and shrinks. The door itself does the same thing on its own schedule, and the house around both of them settles slowly and permanently in one direction.
The result is that the relationship between the bolt and the hole it drops into is not fixed. It drifts. For most of the year the drift is small enough that nothing is noticeable, and then one season it crosses the threshold where the bolt catches on the edge of the strike instead of dropping cleanly through it.
At that point people start doing something they barely notice: lifting the handle, leaning on the door, pulling it towards them. The door still locks, so nothing feels broken. But the bolt is now working against the strike plate every single time, and that grinding is what eventually wears the lock out.
A worn-out lock is very often a symptom. The frame moved first, the lock spent two years fighting it, and then the lock got the blame.
Reading the symptoms
The door has to be pulled or pushed before it locks
The strike has drifted horizontally, or the door has racked slightly. The bolt is meeting the edge of its hole rather than the centre. This is the earliest and cheapest stage to fix.
The door has to be lifted
The hinge side has dropped — usually loose or worn top hinge screws, sometimes a hinge that has bent under a heavy slab. The fix starts at the hinges, not the lock.
The door drags on the threshold or the frame
Either it has swollen, or the frame has moved inwards. Sometimes seasonal and self-correcting, sometimes structural and permanent.
You can see daylight at one corner
The door is out of square in its opening. On a house door that is usually settlement; on a commercial door it is usually the pivots or the top hinge sinking under high cycle counts.
What the fix actually involves
In most cases, very little. Repositioning or filing a strike plate, packing or replacing a hinge, tightening screws that reach real structure, or adjusting the latch. Fifteen minutes to an hour, and no new hardware at all.
Where the jamb has split — usually from a forced entry, sometimes from years of a bolt fighting a misaligned strike — the repair is more involved: the split section is glued and clamped or replaced, and a reinforced strike is fitted and anchored with screws long enough to reach the stud behind the frame.
That reinforcement is worth doing whether or not anything has gone wrong. A standard strike plate is held by three-quarter-inch screws that reach the door trim and stop. The trim is nailed to the frame and the frame is shimmed off the structure, which means a determined kick is resisted by finish carpentry. Three-inch screws into the stud change that completely, and they cost less than a coffee.
The one time it really is the lock
Occasionally the frame is fine and the mechanism has genuinely failed. The signs are different: the key turns freely without moving the bolt, the bolt extends only part way, the handle spins without retracting the latch, or the cylinder turns roughly in both directions even with the door standing open.
That last test is the useful one. Open the door, and operate the lock with nothing to bind against. If it works smoothly with the door open and badly with it closed, the lock is fine and the frame is not. If it works badly either way, the lock is the problem.
It takes ten seconds, and it settles the question before anybody spends money.
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