when I hear a popping sound I know I should have replaced it awhile ago, so I do it then.......I once heard a story about a woman who brought her machine in to the repairman saying it "just would not stitch!" He looked at it and asked how long she had had the machine, she couldn't remember how long, just a "long time", then he asked when she last replaced the needle...you guessed it--never had--needle no longer had a point......