Good afternoon. I recently bought my 1st Hot tub (used). I saw it working correctly before I bought it. Now it wont heat. It is a Sundance Optima that was taken very good care of and serviced annually. The heater test good at 10 ohms and rings out. The issue appears to be K1 relay, it is not switching on, and I can not find which sensor or protocol is calling for the K1 relay.