Controller displays SLO or SLOW RISE and shuts off solar heating because the pool temperature is not increasing as expected.

Safety first: Turn off the pump before adjusting valves or opening unions. Use caution on the roof.

• Check for shading: Inspect the Heliocol array during peak sun to ensure panels are not shaded by trees, antennas, or new structures. Trim vegetation if necessary.
• Bleed trapped air: With the pump running in solar mode, open any manual air relief at the top of the array or slightly loosen a high-point union to purge air until a steady stream of water appears, then retighten.
• Verify valve positions: Ensure the solar bypass or mixing valve is fully directing flow through the Heliocol panels when solar is active.
• Check flow rate: Confirm the pump speed (for variable-speed pumps) is set high enough to provide adequate flow through the collectors as specified by Heliocol design guidelines.
• Evaluate system sizing: If performance remains poor, consult Heliocol sizing charts to determine if additional panels are required for your pool size and climate.