CobbCJ7

I got this hot tub of craigslist from a rich dude near me. He hadn't run it in years. I have managed to make it work but it will not stop the heating process. When it reaches the set temperature, the call for "heat" indicator on the control panel turns off, However, it is still sending 240 volts to the element and turns this tub into a fryer. And or it will burn the element up completely. Now that I am thinking about this as I post, I recall that I found a black very short wire in the bottom of the control box. Since I had no knowledge at the time, I think I may have discarded it or not sure what I did with it since its been over a year.. My question is, am I missing a black wire between the heater relays?? Can you tell me which one if so?? Here is a URL to the full-size image link.. https://ibb.co/Wv11sw1 Thanks!

I have a Catalina 7 person spa with a Balboa Cat-200-DCAJ #51677-05. I got this whole thing for free and it's been a pain in the neck ever since. The only problem I have had so far is that the heater element never shuts off. It will climb all the way to 110deg or more. I've tried setting the temp level down at 90 and it blows right by that. I have burnt up so many elements now. What could be the culprit?? One of the Temp sensors?? Also, if the spa pump shuts down, which for some reason it does on its own. Or if I put it on the Economy mode were the pumps run just a few times a day, that heater element stays on and burns itself up. I don't have the money to go out and buy a $1,400 replacement control box so I was hoping for some suggestions. P.S. I hate to admit that I have smaller gauge wires than what is listed for the tub. It calls for 6 gauge and I am running 10 gauge wires. But, I only have one working pump currently so I don't see the need for the expensive bigger gauge until I get the pump fixed. The reason I added this is to see if for some reason the smaller gauge would affect the mainboard in a way that would not shut off the heater element. I assume not but thought I would add it. Thanks and any help is much appreciated!!