Controller displays CAL or CALIB and temperature readings are obviously incorrect; system may not start or may overheat.

Safety first: Turn off power before opening the controller enclosure.

• Exit calibration mode: Refer to the controller manual for the key sequence to exit CAL mode and return to normal operation.
• Verify sensor type: In the controller setup menu, confirm that the correct sensor type (e.g., 10k thermistor) is selected for both pool and solar sensors used with Heliocol systems.
• Recalibrate if allowed: If the controller supports user calibration, use a known-accurate thermometer in the pool and adjust the displayed temperature to match.
• Power-cycle controller: Turn power off for 30 seconds and then back on to clear any temporary firmware issues.
• Replace controller if unstable: If calibration drifts repeatedly or settings will not save, the controller’s memory may be failing and the unit should be replaced.