Display shows FLC or FLOC and spa may heat erratically or shut down.

Safety first: Turn off power at the GFCI breaker before touching any wiring.

• Inspect flow switch wiring: Open the equipment bay and locate the flow switch near the heater tube. Check that the two wires are intact, not pinched, and properly connected to the control board.
• Check for moisture: Look for water intrusion around the flow switch body or wiring. Dry any moisture and correct leaks before proceeding.
• Test switch operation: With power OFF, disconnect the flow switch leads and test continuity with a multimeter. With no flow (pump off), the switch should be open (no continuity). If it reads closed, the switch is stuck and must be replaced.
• Verify correct part: If the flow switch was recently replaced, confirm that a Marquis-compatible switch with the correct normally-open configuration was installed.
• Replace flow switch: Drain water below the switch level or close isolation valves. Unscrew the switch from the plumbing tee, install the new switch with thread sealant as recommended, reconnect wires, and restore power.

Note: If a new, correct flow switch still shows FLC, the control board input circuit may be defective and require professional service.