Display alternates between FL and temperature, heater does not engage or cycles on and off frequently.

Safety: Turn off power at the breaker before removing panels or touching wiring.

• Clean filter thoroughly: Remove the filter and soak it in a filter cleaner solution according to the product directions, then rinse well. Test the spa with the filter removed to see if FL clears.
• Inspect circulation pump performance: With power on, verify a steady stream from the circulation return jet. Weak or pulsing flow suggests a failing circ pump or partial blockage.
• Check pressure switch wiring: Power off. Remove the front panel and locate the pressure switch on the heater tube. Ensure spade connectors are tight and free of corrosion. Clean contacts lightly if needed.
• Inspect heater manifold: Look for kinks in hoses or crushed flex pipe near the heater. If accessible, remove unions and check for debris or scale buildup inside the heater tube.

If the FL code appears only when jets are on high speed, the system may be borderline on flow and the circulation pump or pressure switch should be tested and possibly replaced.