Control panel displays FLO and the heater will not turn on; circulation pump may or may not be running.

Safety first: Turn off power at the GFCI breaker before opening the equipment bay or touching any wiring. Never run the spa with valves closed.

Step-by-step:

• 1. Check water level: Ensure water is above all jets and at least halfway up the skimmer opening. Low water can cause a FLO error.
• 2. Clean the filter: Remove the Sundance MicroClean or pleated cartridge filter from the filter well. Rinse thoroughly with a garden hose from top to bottom. If heavily soiled or older than 1 year, replace it.
• 3. Bypass the filter test: With power OFF, remove the filter and briefly power the spa back ON for 1–2 minutes. If FLO clears with the filter removed, the filter is restricted and must be cleaned or replaced. Turn power OFF again before reinstalling.
• 4. Bleed air from the system: If the spa was recently drained/refilled, loosen the union on the circulation pump or open the bleed screw (if equipped) until water flows steadily, then retighten. This removes air locks.
• 5. Inspect the flow switch: Locate the flow switch in the heater plumbing (usually a tee with two small wires). Check that the wires are firmly connected and that the body is not cracked or leaking. Do not jumper the switch for normal use; this is a safety device.
• 6. Check circulation pump operation: With the equipment bay open and power ON, verify that the 24‑hr circulation pump is running (you should feel vibration and see water movement in the heater tube). If it is not running or is noisy/hot, it may be failing.
• When to call a technician: If FLO persists after filter cleaning, air bleeding, and confirming water level, the flow switch or circulation pump likely needs replacement and wiring/voltage checks should be performed by a qualified spa technician.