Controller displays LO or LOW TEMP and refuses to open the solar valve, even on warm sunny days.

Safety first: Turn off power to the controller before handling sensors or wiring. Use proper fall protection on the roof.

• Check sun exposure: Verify the solar sensor is located on the same roof plane as the Heliocol panels and is not shaded by chimneys, trees, or other structures.
• Confirm contact with header: Ensure the sensor is firmly attached to a header pipe that carries water through the Heliocol collectors, not to a cold return line or a mounting bracket.
• Inspect wiring connections: Tighten sensor terminal screws at the controller and repair any damaged cable sections.
• Compare temperatures: On a sunny day, compare the controller’s solar temperature reading with an infrared thermometer aimed at the header. If the reading is significantly lower, replace the sensor.
• Re-test system: Restore power and verify that the LO indication clears when the roof warms above the pool temperature.