How exactly did you check the fuses outside of the system? Fuses cannot merely be tested for continuity but, should be tested for voltage on the circuit board with power live. If you are getting anything but 0 voltage then you have a bad fuse. I can tell you right now that nothing is going to heat if your circulation pump is not running. The fact that it is not running is an immediate red flag to me. Since you have confirmed the circ pump to work, you need to figure out why it is not running. Your circ pump should turn on immediately. Are you getting power on the circuit board where your circ pump plugs in? Confirm whether or not you are getting voltage between the white and black on the circuit board where the circ pump connects. https://www.sundancespas.com/media/3414/850-series_english-2.pdf If this diagram on page 33 matches your circuit board, it would be at TB2. In my humble opinion, if you are not getting power to your circ pump from the board, and the pump is confirmed to work, then perhaps you have a bad capacitor on board.
Ooops sorry. I just typed this all out, only to realize you had discovered the bad capacitor.