Breaking thread is super annoying. It happens for many reasons, none of which are any less irritating. Here are my top tips. Start from number one and work through them until it is solved.
  1. Get a cup of tea and settle down to fix the problem. When I am stressed, I can never fix problems.
  2. Is the stitch length correct? Are you using too small a stitch on a thick fabric or seam? Stitches will burst if the material is too thick for the size of the stitch. Bursting stitches can appear as if the thread is breaking. Thicker fabric will need a longer stitch, and a bulky seam may need the stitch length altered to flex over it.
  3. Remove both top and bottom threads from your machine, rethread and test.
  4. I am assuming that is your top thread breaking. Cut a piece of this thread and see how hard it is to break by pulling it with both hands. If easy, then this is not a good thread to use in your machine. Find a better thread. If it is the bobbin thread, do the same.
  5. Check that you have the same weight or thickness of thread in the bobbin and top of your machine. If one is thicker or thinner than the other, it can cause problems. To test this wind, a bobbin of the top thread and continue sewing. If not, use the bobbin thread as the top thread, replace this bobbin (same thread) and test with this thread.
  6. Is your machine clean? Have a look at my maintenance guide below.
  7. Are you using the right needles? Does it need changing?

By now you will need another cup of tea, but I hope we have solved the issue. By far, most of the thread breaking problems I have found are solved by working through these steps.