Controller shows SEN or SENSOR ERROR; solar heating is disabled and system runs in bypass only.

Safety: Turn off power to the Fafco controller before opening the enclosure or touching wiring.

• Identify which sensor: Many Fafco controllers indicate whether the pool or roof sensor is faulty. Refer to the display or manual.
• Inspect wiring: Open the controller cover and locate the sensor terminals. Tighten any loose screws and look for corrosion or broken conductors. Clean light corrosion with a small brush.
• Check continuity: Disconnect the suspect sensor leads and use a multimeter to measure resistance across the sensor. An open (infinite) or near-zero reading indicates a failed sensor or shorted cable.
• Trace cable path: Follow the sensor cable along the plumbing or up to the roof. Look for staples through the cable, UV damage, or rodent chewing. Repair or replace damaged cable runs.
• Replace sensor if needed: Install a genuine Fafco-compatible temperature sensor, matching the original type (usually 10k thermistor). Connect to the correct terminals and secure the cable.
• Restore power and test: Power up the controller, verify the SEN code clears, and confirm that both pool and roof temperatures display realistically.