Topside control shows FLO or FL1 and the hot tub will not heat; pump may run briefly then stop.

Safety first: Turn off power at the GFCI breaker before opening any equipment bay or touching wiring. Never run the spa with valves closed or without water.

• Check water level: Ensure the water level is above all skimmer openings and filter weirs. Low water can cause a FLO error.
• Clean or remove the filter: Remove the Hydropool filter cartridge from the skimmer or filter housing. Rinse thoroughly with a garden hose from top to bottom. For testing, run the spa briefly without the filter (with power restored) to see if the FLO error clears. If it clears, replace the filter.
• Bleed air from the system: After a refill, air can be trapped in the circulation lines. With power OFF, loosen the union on the circulation pump or heater manifold slightly until air hisses out and water begins to seep, then retighten. Restore power and check if FLO clears.
• Verify pump operation: With the cabinet panel removed and power ON, confirm the dedicated circulation pump (or low-speed on Pump 1, depending on model) is running smoothly and water is visibly moving in the spa. If the pump hums but does not move water, it may be air-locked or failing.
• Inspect the pressure/flow switch: On many Hydropool models, a pressure or flow switch is mounted on the heater manifold. With power OFF, check that the wires are firmly connected and that there are no kinks in the plumbing. If the switch is adjustable, do not overtighten; if it is stuck or corroded, replacement is recommended.
• When to call a technician: If the FLO error persists after filter cleaning, air bleeding, and confirming pump operation, the circulation pump or flow/pressure switch may need replacement and should be tested with a meter by a qualified spa technician.