Sarah, It might be that the zipper pull has "opened up". This can happen by forcing the zipper or just from use. It last happened to my 15 year old down vest. Give this a try. First make sure the zipper and pull are not damaged. If they appear to be OK take a needle nose pliers and carefully squeeze the fat (lead) end of zipper pull to slightly lessen the gap the zipper and zipper tape need to go through. It works for me if everything else looks good. Good Luck