Q: Why does my zipper keep jamming near the slider?
A jam near the slider almost always means the chain is not entering the slider at the correct angle or the channel is obstructed. Common causes are a bent or deformed tooth, a tape edge folded into the channel, lint and sand packed behind the slider, or a slider that has been spread by angled pulling. A mismatch between slider size and chain size produces the same symptom from the first use.
Diagnose by moving the slider to a clean section of chain. If it runs freely there, the problem is local: inspect the teeth at the jam point under a loupe and look for a raised tooth or a damaged tape edge. If it jams everywhere, measure the slider gap and compare it with a new slider of the same specification.
Correct the cause, not the symptom. Replace a deformed slider or tooth, trim a folded tape edge, and clean the chain with a soft brush and mild soap. Never force a jammed slider with pliers, because the body distorts and the jam returns. In production, check the seam allowance near the slider and the condition of the zipper foot, since a needle strike is a frequent source of a raised tooth.