As the opening increases in size, it puts less pressure on the tracts of the zipper, allowing them to stay separated.
In some cases, bent teeth on a zipper will cause a zipper to separate. If the zipper teeth are metal, you can use a pair of pliers to straighten them out. If the teeth are plastic, gently try to straighten them with your fingers, as pliers could easily break them off.
On one end of the slider there is a middle piece that won’t let you squeeze it. On the other end there is no middle piece. That is the side that gets opened and needs to be squeezed back together. Don’t squeeze the slider too strongly though, as you don’t want to make the gap smaller than it should be. You will know the gap is too small if it becomes difficult to pull up and down the zipper slider along the tracks.
If the zipper still doesn’t work, either squeeze the slider more or try another solution. [3] X Research source
The stops at the top of the zipper are small pieces of metal that are shaped a bit differently from the teeth on the zipper. They are not big pieces and they look similar to teeth but they are slightly larger and are positioned at the very end of each side of teeth. If the stops are plastic, you won’t be able to take them off and put them back off without breaking them, so you can’t use this method.
It’s important to be gentle with the stop and don’t cut it or bend it until it breaks. You need to keep it intact. Keep the top stops and put them somewhere safe, as you’ll need to use them again.
Put the zipper on top of a hard surface. As you work your way up the zipper, press down on the teeth to pop them into place. It is important that the teeth are perfectly lined up. Make sure that once you get to the top of the zipper that you don’t have extra teeth on one side. This would mean that the teeth are not lined up.
You will know each side is inserted when several teeth have gone up into the slider and the track won’t go any further. It’s easiest to insert one side and then the other. Putting them both in at once doesn’t typically work.
Be sure not to pull the slider all the way back up to the top, as it will slide off of the tracks again without the top stops in place.
Wiggle each stop after you reinstall it to ensure that it is securely in place.
