Safety: Turn off power at the GFCI before working on plumbing or electrical components.

Check water level: Ensure water is above the skimmer and all jets. Top up if needed.
Clean filters: Remove Canadian Spa Company filter cartridges and rinse thoroughly. For testing, you can run the spa briefly without filters to see if FLO clears.
Bleed air locks: With power OFF, loosen the pump union or the bleed screw (if present) on the circulation pump until water flows steadily, then retighten.
Inspect flow switch: Locate the flow or pressure switch near the heater tube. Check wiring connections for corrosion or looseness. Ensure the switch body is not cracked or leaking.
Test circulation: Restore power and run the pump. Confirm strong flow from heater return jets. If flow is weak or noisy, the circulation pump may be failing.
Bypass test (for technicians only): Temporarily jumping the flow switch for testing can confirm a bad switch, but this should only be done by a qualified technician due to safety risks.

If FLO persists after cleaning filters, bleeding air, and confirming good water level, the flow switch or circulation pump likely needs replacement.

Display shows FLO or FL and heater will not turn on; may show intermittent heating.

Possible Causes