The breaker is a good choice. Also if you are using the "thin" style breakers, (these are the ones that fit two to a socket) they will work poorly. If it is a GFI type breaker they work poorly and die frequently. You may have to try more than one replacement to verify the breaker problem. When installing our spa the first two from the local Home center ran hot, emitted a stench and were down right scary. I had to go with one from an electrical distributor and it has worked properly. Beware of cheap junk.
Good luck, John
Good luck, John