I have an older Arctic Spa, Arctic Fox, and having difficulties troubleshooting the HL error code. The HL code appears (solid) whenever the tub reaches the selected set point temperature. We tested different set points from 80 to 100 deg and each time the water reaches the set temp the display changes to HL and the heater turns off instead of maintaining the temp and going into filter mode. We have replaced the heat probe and filter and both pumps are functioning. I am wondering if this is a heater/thermostat/probe issue or CB one? Thank you for any guidance you can offer.