I usually find that when the thread is bunching up on me on the bobbin side it is because my top thread has slipped out of the thread race somewhere. Try rethreading your spool on top again. Also, I am wondering what it is you are doing at the moment? Is it piecing or is it FMQ? If FMQ then are you pulling the bobbin thread to the top before you begin? Maybe you have done all of these things already. If you are adjusting the bobbin tension the you probably know that left is loose and right is tight? Good luck.

The pressure foot must be UP when you bring the thread through the tensions disks , pull a good amount of thread through, then lower the pressure foot and finish threading.

Problems under fabric are usually threading issues on top. Thread not seated in tension disks is a common error.

Hi, I don't have a Bernina but it sounds like a top tension problem.
Hope this helps, good luck
Anne

I have a Bernina Activa 230.... Bought it new about 2 yrs ago, just really starting sewing and this weekend the bobbin thread started bunching up. I have done everything I know to do; Rethread the bobbin, take it out, put in back in... several times. Turned the screw in the bobbin case (just a little)... Nothing seems to work.

Can anyone help me?

Lost in Texas,
Rhonda