Controller displays SEN or SENSOR and solar heating is disabled even on sunny days.

Safety first: Turn off power to the solar controller before opening the enclosure or handling sensor wiring. Use a stable ladder and fall protection when accessing the roof.

• Inspect controller connections: Open the Heliocol-compatible solar controller and locate the solar (roof) sensor terminals. Tighten any loose screws and ensure the sensor wires are firmly clamped.
• Check sensor cable condition: Follow the sensor cable from the controller up toward the roof. Look for cuts, rodent damage, or UV cracking. Repair minor damage with waterproof splices or replace the cable if extensively damaged.
• Test sensor resistance: With power off, disconnect the sensor leads and measure resistance with a multimeter. Compare the reading to the temperature/resistance chart in the controller manual. Infinite or near-zero resistance indicates a failed sensor.
• Inspect roof sensor: On the roof, verify the sensor is firmly attached near the Heliocol panel header and not sitting in standing water or shaded. Replace the sensor if the housing is brittle, cracked, or waterlogged.
• Reset and test: Reconnect wiring, restore power, and clear any error by cycling controller power. Confirm the SEN code disappears and the controller reads a realistic roof temperature.