Hydro-Quip · Hydro-Quip digital control systemsFix soon

FLO on a Hydro-Quip hot tub: flow or pressure switch

The pressure switch is not seeing proper water flow, so the heater is off. The tub is safe to use but will not heat.

Also shown as: FL, FLOW

Most likely causes

  1. 1Dirty or clogged filtermost likely
  2. 2Low water or an air lockcommon
  3. 3Pressure switch failed or out of adjustmentcommon
  4. 4Pump not running or weakless common

What to try, in order

  1. Check the water level.
  2. Turn off power at the breaker, remove the filter, and rinse it.
  3. Restore power and test with the filter out. If the code clears, the filter is the cause.
  4. Bleed any air lock after a refill.
  5. If flow is strong and FLO remains, the pressure switch likely needs replacing.

FLO questions

Can I use the hot tub with FLO showing?

Yes, but the heater is disabled. Fix it before the water gets cold.

Where is the pressure switch?

It is a small switch threaded into the heater tube or the plumbing near it, with two wires going to the control box.

Related codes

Balboa FLO · Low water flowGecko FLO · No water flow detectedJacuzzi / Sundance FLO · Flow switch problemHydro-Quip OH · Overheat protectionHydro-Quip Sn1 · Hi-limit sensor faultHydro-Quip Sn3 · Temperature sensor fault

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