Display shows FLO or FL and heater will not turn on; sometimes pumps run but no heat.

Safety first: Turn off power at the GFCI breaker before removing filters or opening the equipment bay.

• Step 1 – Check water level: Ensure the water level is above all jets and suction fittings. Low water can cause air ingestion and low flow.
• Step 2 – Clean filter: Remove the Nordic filter cartridge. Rinse thoroughly with a garden hose from top to bottom. For testing, run the spa for 10–15 minutes with the filter removed. If FLO clears, replace the filter with a new Nordic-compatible cartridge.
• Step 3 – Bleed air from system: If the spa was recently refilled, loosen the pump unions and heater unions slightly to release trapped air until water appears, then retighten. Make sure all slice valves are fully open.
• Step 4 – Verify pump operation: With power on, confirm the circulation pump or low-speed of the main pump is running when the spa calls for heat. Listen for humming without water movement (sign of a seized pump). Check for strong flow at the heater return jet.
• Step 5 – Inspect flow/pressure switch: Locate the flow or pressure switch on the heater plumbing near the Nordic control pack. Check for loose wires or corrosion. With power off, disconnect and test continuity across the switch while the pump is running (requires a multimeter and basic electrical skills).
• Step 6 – Replace faulty components: If flow is good but FLO persists, replace the flow switch or pressure switch. If the pump is weak or not running, replace or rebuild the circulation pump.