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

Safety: Turn OFF power at the GFCI breaker before opening the equipment bay or disconnecting anything.

• Check water level: Confirm water is at or slightly above the recommended fill line.
• Clean or remove filters: Remove all filters and run a thorough hose cleaning. For testing, leave filters out temporarily after you restore power to see if FLO clears.
• Bleed air from circulation pump: With power OFF, loosen the union on the circulation pump until air escapes and water seeps out, then retighten.
• Locate the flow switch: On most Michael Phelps Spas, the flow switch is installed in the plumbing line near the heater manifold with two small wires going to the control pack.
• Inspect flow switch wiring: Check that the two-wire connector is firmly seated on the control board and that the wires are not damaged.
• Check for stuck paddle (if accessible): Gently tap the body of the flow switch with the handle of a screwdriver to free a stuck paddle.
• Restore power and test: Turn the breaker ON. Run the pump and observe if FLO clears. If FLO clears with filters removed but returns when filters are installed, replace the filters.
• Replace flow switch if needed: If there is good flow and clean filters but FLO persists, replace the flow switch with an OEM Michael Phelps/ Master Spas-compatible flow switch. Shut power OFF, drain below the switch, cut or unscrew the old switch, install the new one in the same orientation (arrow in direction of flow), reconnect wires, then refill and bleed air.