UltraVegas

We rented a house with a spa for the last 3 years. Owners wanted to get rid of the spa since it didn't work but we said we would like it to stay to see if we could get it to work. We initially tried to see what was wrong but gave up (never put too much effort in). I am new to spas so please forgive me... Problem is that every time you turn the breaker on it would trip right away. I started this time by process of elimination. I disconnected everything until it stopped tripping. I finally found that when the High Limit sensor is plugged into the circuit board it trips everytime. I reconnected everything but the HL sensor and it has been running without tripping for 2 days now. The only thing is I see HL on the Controller screen. Should I replace just the HL sensor or could the issue be deeper than that? Can we use the spa even with it disconnected. Seems to work fine except the water doesn't heat which isn't a big deal right now since the temp here is getting to above 100 soon. Secondly, it say it's LA Spa and the model number says 1/01CA Paradise but I can't find any info about the spa anywhere, no even on the LA Spa website... Thanks in advance for any help!