Usually means the pcboard isn't seeing the water flow or the water flow isn't there.

If the #1 or circulation pump is NOT operating, the FL1 error will come on. You need to first address the pump. If you do not see water moving then likely the pump has failed. You likely need to replace the pump/motor. To confirm this you would do a voltage check to see that proper voltage is being applied to the pump.

If the #1 pump IS operating, try removing the filter(s) to confirm that isn't the problem

If the #1 pump is operating, filters are out, and the FL1 error is there, it's could be the flow or pressure switch, depending which your spa has OR the pcboard.

First and most common is the pressure switch. Because this interrupts use of heater, it's always best to replace. If not the pressure switch, it's the pcboard itself but this is rare. I would always recommend simply replacing the switch first.

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