Controller flashes POOL or POOL SEN and will not allow solar heating; pool temperature reading is blank or unrealistic.

Safety first: Turn off power to the solar controller and pump. Close valves if removing any in-line sensor.

• Verify sensor location: Confirm the pool sensor is installed in the plumbing after the filter and before the solar tee, as recommended for Heliocol systems.
• Inspect wiring: Open the controller and check the pool sensor terminals. Tighten screws and ensure no bare wires are touching adjacent terminals.
• Check cable integrity: Trace the sensor cable from the plumbing to the controller. Repair any visible cuts or abrasions using waterproof connectors or replace the cable if necessary.
• Test sensor: Disconnect the sensor and measure resistance with a multimeter. Compare to the manufacturer’s temperature/resistance chart. Replace the sensor if readings are out of range or unstable.
• Replace in-line sensor (if leaking or failed): Depressurize the system, unscrew the sensor from its well or tee, apply new thread sealant or O-ring as required, and install the new sensor. Restore flow and check for leaks.
• Power up and verify: Restore power and confirm the controller now displays a realistic pool temperature and the POOL error clears.