A failure of either the flow or pressure switch
usually creates an error code on our topside. Common
flow error codes are FL, FLO, PS1, PS2, or the like.
If you are getting that error it could be the
pressure of flow switch.
Your hot tub has either
a pressure switch or flow switch. The purpose of either is
simple: tell the board if you have enough water
moving to turn the heater on. Its the spas first
protection from causing a meltdown or fire because
of lack of water flow.
Your control system will likely follow this order:
When you first power up and all pumps are off it
will check the flow or pressure switch. Because of
no water flow the switch on most models should be
OPEN. If closed you will get some FLOW error. Often
its a solid flow error but see your manual for help.
What the unit does is "looks" at the switch before
it turns the pump on. If the switch is closed the
spa will see that as a fault and either completely
not come on or only partially. And give you a
pressure/flow switch error.
If the spa passes the first test it will turn on the
circ pump or low flow pump and AGAIN look at the
pressure/flow switch. Now the switch should be
CLOSED. If it is the control will turn on the
heater. If the switch is not closed the control will
not turn on the heat and give you another FLOW
NOTE: If the flow error only comes on AFTER the pump
comes on and you can SEE the pump come on and water
moving, try removing filter(s) and see if that
resolves. If not, see adjusting the flow switch