Q: Why does my zipper open from the bottom by itself?
A closed zipper that splits from the bottom is usually a locking or slider-gap problem rather than a tooth problem. Check the slider first, because replacing a chain that is sound wastes time and does not remove the cause.
- Close the zipper fully, then pull the two tapes apart at the bottom with moderate hand force and watch where separation starts.
- Measure the slider gap and compare it with the maker's limit; an opened gap is the most common cause.
- Check that the bottom stop is present, correctly positioned and not cracked.
- Inspect the first few teeth above the stop for wear, because a worn pair lets the slider ride up.
- Confirm the slider is the size marked for the chain; a mixed slider is an assembly defect.
If the gap is within limit and the stop is sound, look at garment tension, since a tight waistband can lever the slider open. Replace the slider only after the gap measurement and a photograph are recorded, so the maker can see the evidence rather than a description.