There are several reasons why thread breaks. Is your thread old? If so, replace your thread. Good quality thread is so important. I use Mettler in my sewing machine and I use OMNI made by Superior. You can test your thread strength by wrapping the thread around a couple fingers and pull. You shouldn’t be able to break the thread. If the thread breaks replace it. If you have determined that your thread is good quality, review your machine settings. Check the upper tension and the bobbin tension. Sometime you just need to rethread your sewing machine as sometime there can be a miss threaded machine.