Display shows FLO or FL1 and heater will not turn on; may show intermittent flow errors
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Turn off power at the GFCI breaker before removing filters or opening unions.
FLO/FL1 means the control system does not detect adequate water flow through the heater.
- Clean or replace filter: Remove the American Whirlpool filter cartridge and rinse thoroughly. If the cartridge is older than 1 year or shows signs of collapse, replace it.
- Check water level: Ensure the spa is filled to the proper level so the skimmer and suction fittings are fully submerged.
- Bleed air from pump: Loosen the union on the circulation pump until water seeps out, then retighten. This removes trapped air that can prevent priming.
- Inspect flow switch: Locate the flow switch in the plumbing near the heater (a small tee with wires). Check that the wires are intact and the switch body is not cracked or leaking.
- Test flow switch operation: With power on and pump running, gently tap the flow switch body. If the FLO code flickers or clears temporarily, the switch may be sticking and should be replaced.
- Check circulation pump: Listen for the circ pump running. If it hums but does not move water, the impeller may be jammed or the motor failing.
If cleaning the filter and bleeding air do not resolve FLO, replacing the flow switch or circulation pump is often required. Have a technician verify flow and heater safety before extended use.