First, the pressure switch has
nothing to do with pressure in the spa. It's
sole purpose is to tell the pcboard whether to
turn on the pump and then whether to turn on the
heater. Simply stated, when you first turn on
main power or when the spa is about to turn on
the heater/circ pump, the pcboard checks the
pressure switch to confirm the micro switch is
open. If it is not, then the topside either says
solid FLO or FL or the heater light blinks 9r or
nothing at all.
If it is open, then the pcboard turns
on the #1 pump or circ pump. Shortly after the pcboard now
looks to the pressure switch to see if the micro switch is
closed. If so, it turns on the heater. If it is not, the
topside either now flashes FLO or FL, or the heater light
flashes, or on some pcboards, everything looks OK but the
heater light does not come.
So you can see there is a narrow
adjustment on the pressure switch that will make sure it's
open when the spa is off and close when the pump is one.
This leads to a common problem: quality of pressure
switches. Our recommend switches are more expensive but
reliable. The cheaper the switch, the reliability the switch
If your spa does not have a pressure
switch, it will have a flow switch. The purpose is the same
as above but rather than having a part with a diaphragm and
micro switch, you have a simple switch that as water passes
by closes the switch and completes the circuit. IF not
enough water goes by or the switch is broken, it won't allow
the heater to come on.