Flow messages on the control panel that indicate FLO or FL or similar can mean a few different things, but if it is time to replace the pressure switch, be sure to replace it with a similar type. You don’t automatically need to exchange the pressure switch (if your system has one) because there is a FLO error code. In order of priority, first establish that there is not actually a flow restriction. Is the filter dirty? Is there an obstruction covering one of the suction intakes or other part of the plumbing? Was the unit operated without a filter and something got stuck in the line or pump? Is there proper voltage to the spa? Was the spa recently refilled and there may be an air lock or pocket preventing the circulation pump from priming properly?
Hot Tub Pressure Switches
A hot tub pressure switch is found in many spas, especially older units as newer ones that use Balboa packs have gone to the integrated sensors within the heater system. The pressure switch is a safety device that monitors water flow through the heater tube and if there is a restriction or pressure problem, the switch sends a signal to the circuit board to disconnect power to the heater. Pressure switches have a calibration thumbwheel so that the pressure that triggers the switch can be adjusted.
If the spa will not heat and there is an error code, you may just have a pressure switch problem.
Prepare to exchange pressure switch if the problem is with the switch and it cannot be adjusted.
Another way to check if the pressure switch is bad is by disconnecting it and measuring the ohms across the terminals, then adjusting the thumbwheel to see if it changes at a certain part. This is similar to calibrating the pressure switch by meter. If there is no continuity, you will have an open circuit and the switch will be off. Once there is no continuity on the ohm meter, edge the thumbwheel (counter-clockwise) until you get continuity on the meter by seeing some type of resistance between the terminals on the pressure switch. At this point you would turn the thumbwheel clockwise about 1/2 turn so that it does not have continuity again and that would be the setting to use.
Adjusting the Pressure Switch
Adjustments are made to the pressure switch by the black thumbwheel on the switch. Turning the wheel counterclockwise makes the switch more sensitive to changes in water pressure within the heater manifold and eventually turns the switch off, creating an open circuit. Adjustments are made to the pressure switch with power to the spa OFF.
*Info provided for information purposes only. Seek qualified help when working on any electrical appliance or product including a hot tub.