I have a Jacuzzi Cirrus spa, vintage 1993. My heater is not working, and I have figured out that there are two relays wired in series right next to each other at the top of the control panel. Everything is OK except the relay on the left is not closing to close the heater circuit. the one on the right opens and close with the temp controller, and the flow switch, which also controls the relay on the right, is working fine. What controls the left hand relay? Any ideas out there?

USUALLY (and I do mean usually, yours may be different) there is only one relay in charge of the heat. If you have a multitester, check for voltage at the heater. If you have power there, you have a bad element. If not, then it is POSSIBLE that other relay is in charge too, but I haven't personally ran across a system using 2 relays before, so I can't help ya there.