Balboa · Older Balboa and VS / GS systems that use a pressure switchFix soon

FLO on a Balboa hot tub: low water flow

The pressure switch is not seeing enough water flow through the heater, so the heater is turned off. The tub is safe to sit in, but it will not heat until flow is restored.

Also shown as: FL, FLOW, Flo flashing

Most likely causes

  1. 1Dirty or clogged filtermost likely
  2. 2Low water level or an air lock after a refillcommon
  3. 3Closed slice valves or blocked suction coverscommon
  4. 4Failed or out-of-adjustment pressure switchless common
  5. 5Weak or failed circulation pumpless common

What to try, in order

  1. Check the water level. It should be above the highest jets and at least halfway up the skimmer opening.
  2. Turn off power at the breaker, pull the filter, and rinse it. Restore power and run the tub briefly without the filter to see if the code clears.
  3. If the code clears with the filter out, clean the filter in a filter cleaner soak or replace it.
  4. If you just refilled, bleed the air lock: open all jets and pulse the pump between low and high for 10 to 15 seconds at a time.
  5. Make sure any slice (gate) valves next to the pump and heater are fully open and nothing is covering the suction fittings.
  6. If the pump runs with good flow and FLO stays, the pressure switch is the likely part.

FLO questions

Can I use the hot tub with a FLO error?

Yes, the water is safe to sit in if your sanitizer is in range, but the heater is locked out, so the water will cool down. Fix the flow problem before the tub gets cold, especially in freezing weather.

Why does FLO show up right after I change the water?

Air trapped in the pump or heater after a refill stops water from moving. Bleed the air lock and the code usually clears within a few minutes.

What is the difference between a flashing and a solid FLO?

On many Balboa systems a flashing FLO means the switch did not close when the pump started (not enough flow). A solid FLO means the switch is closed when the pump is off, which points to a stuck or failed pressure switch.

Related codes

Gecko FLO · No water flow detectedHydro-Quip FLO · Flow or pressure switchJacuzzi / Sundance FLO · Flow switch problemBalboa -- · Temperature not yet knownBalboa CHEK PH · Maintenance reminderBalboa CLN FLTR · Filter reminderBalboa CNFG FAIL · Configuration errorBalboa dr · Heater may be dry

General guidance. Follow your manufacturer's instructions; anything inside the control box is work for a licensed professional. Updated October 5, 2026.