Display shows FLO or FL1; heater will not turn on; may show intermittent flow icon

Safety: Turn off power at the GFCI breaker before working on the spa.

• Clean filters: Remove all filters and rinse thoroughly. If they are more than 1–2 years old or show signs of collapse, replace them with Bullfrog-approved filters.
• Check water level and valves: Ensure water is at the proper level and all slice valves near the pumps and heater are fully open.
• Bleed air from circulation pump: Loosen the union on the suction side of the circulation pump until water flows steadily, then retighten. This removes airlocks that can prevent flow.
• Inspect flow switch: Locate the flow switch in the plumbing near the heater tube (a small tee with wires). Check that the wires are intact and the connector at the control board is firmly seated.
• Test circulation pump: Restore power and observe if the circulation pump runs during heating/filtration. You should see steady water movement at the heater return. If the pump is silent or only hums, it may need replacement.
• Bypass test (advanced, optional): With power OFF, disconnect the flow switch from the board and temporarily jumper the two pins to simulate a closed switch. Restore power briefly to see if FLO clears and heater engages. Do not leave the spa running with the flow switch bypassed; this is for diagnosis only. If FLO clears with the jumper, replace the flow switch.

If FLO persists after ensuring good flow and replacing the flow switch, the control board input or circulation pump circuit may be faulty; contact a Bullfrog service technician.