Jacuzzi / Sundance · Jacuzzi J-300 / J-400 and later Sundance seriesFix soon

FL1 on a Jacuzzi / Sundance hot tub: no flow detected

The flow switch is open when the pump is running, meaning water is not flowing properly through the heater. The heater is off but the tub is safe to sit in.

Also shown as: FL 1, FLO1

Most likely causes

  1. 1Dirty or clogged filtermost likely
  2. 2Low water level or an air lockcommon
  3. 3Failed circulation pumpcommon
  4. 4Failed flow switchless common

What to try, in order

  1. Check the water level.
  2. Turn off power at the breaker and clean or replace the filter.
  3. Restore power and listen or feel for the circulation pump running.
  4. Bleed any air lock after a refill.
  5. If the code returns with a clean filter, book service.

FL1 questions

What is the difference between FL1 and FL2?

FL1 means the flow switch is open when the pump is on (no flow). FL2 means it is closed when the pump is off (stuck switch).

Will the tub freeze with FL1?

It can in freezing weather, because the heater is off. Fix it quickly or keep the equipment bay warm with a safe heat source.

Related codes

Jacuzzi / Sundance -- · Watchdog shutdownJacuzzi / Sundance COOL · Water 20°F below setJacuzzi / Sundance FL2 · Flow switch stuck closedJacuzzi / Sundance FLO · Flow switch problemJacuzzi / Sundance HOLD · Panel buttons locked outJacuzzi / Sundance ICE · Freeze protection activeJacuzzi / Sundance OH · Overheat protectionJacuzzi / Sundance Sn1 · Hi-limit sensor fault

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