Pressure Switch/Flow Switch Function
All hot tubs are equipped with pressure or flow switches. While there are technical differences between the two switches, they essentially provide the same function, and the terms are often used interchangeably. These devises are on/off safety switches that will allow power to pass, provided that there is enough water pressure in the system. The pressure switch will automatically turn off the hot tub heater if there is not sufficient water flow to prevent the system from burning up. Consequently, the water will not heat and the hot tub will display the FL0 warning.
Frequently, water obstruction from a dirty or clogged filter is to blame. The filter pleats will begin to restrict water flow if they are not regularly cleaned. A low water level may also cause the FL0 error code. Occasionally, wiring to the pressure switch comes loose. The worst case scenario, which will necessitate replacement of the pressure switch and possibly the heater, is if rust or corrosion has formed on the switch.
There are a few basic things hot tub owners should do before contacting a hot tub repair technician. Check the water level. Verify that the filter well is completely submerged; if it is not, add more water. If the error code remains, turn off all power to the hot tub. Remove the filter, clean it if necessary, and turn on any jets that are closed. Leave the hot tub off for approximately 30 minutes to clear the sensor memory. If a restricted jet flow or a dirty filter was the problem, your hot tub should function normally once the hot tub is powered on again, and the error code will disappear.
More Advanced Solutions
Of course, the problem could stem from the pressure switch itself. Check the pressure switch. Verify that no wires are loose and the part is not corroded. Next, place an electrical meter over the heater element to determine whether you have sufficient voltage running through the system, which is either 110 volts or 220 volts, depending on the voltage of the control box. If the pump is receiving the correct electrical voltage, replace the malfunctioning pressure switch.