I have a similar issue.I have acquired a Jacuzzi spa, and I am experiencing some problems. It is a z145/345, 240000. It has a Balboa board R574 with a 4kw heating element. It was wired for 115v, and I field converted it to 230v system, following instructions labeled on the inside cover of the control unit. I installed it using a 50w GFCI dedicated circuit breaker, with a 60 amp rated disconnect outside. All things are wired correctly. Pump works correctly, topside controls work correctly, and I heat very well. The problem I have is overheating of the water. The high limit sensor worked, because when it hit 112 degrees, power was shut off to the whole unit. I have tested the power output to the heater, and it is always on, even after reaching set point. When the water reaches the set point, the LED light on the topside controller shuts off, I can hear a contactor release, but 240 stays going to the heating element. I tried a new temp sensor, and had no success. I followed recommendations online, disconnected the topside controller after reaching set point, and still no success. I can manually release one contactor, and 240w is eliminated from the heater, but 120w remains. Something is not telling the heater to turn off, and I am wondering what else I can look for. You can try any of the things I did, but I am still having no luck. I will keep you informed if anyone replies to my post as well.