First the background:
I just installed a brand new United Spas Control box and digital topside in a used Leisure Bay tub (recently "inherited"). Originally the heater was plumbed to the suction side of the pump, which I didn't like. However, hoping to avoid replumbing it (since the pump and heater unions are not the same size), I hooked it up the same way. Since the very first startup, I have that friendly "FLO" error on my digital readout which indicates that the pressure switch is not registering any flow. I tried removing the filter and running the pump at both low and high speeds, but the error persisted. I also tried reseting the unit by cutting the power, but no good.

My Configuration:
TUB----> FILTER----> HEATER & SWITCH----> 2-SPEED PUMP----> TUB

Now my question(s):
Could the flow error be a result of the heater (and pressure switch) being located on the suction side (i.e. low pressure side) of the pump? Would replumbing it so that the heater is on the discharge (i.e. pressurized) side of the pump solve this problem?

Anyone have their unit plumbed like this (heater & pressure switch on suction side)? Does your pressure switch work in this configuration?

THANKS!!

If it is indeed a pressure switch, and not a vacuum switch, your diagnosis is right on the mark....

Try checking the ohm's across the switch when there is no vacuum. If it reads OL (open line, ie no contunuity), that's good. Then, turn on the pump (and create a vacuum), if it still reads OL, it is either a bad vacuum switch, or a pressure switch that in the wrong spot. Instead of going through the trouble of re-plumbing, look for a vacuum switch with identical threads. (1/8"?) Pres:Air:Trol makes one.
It's an unusual part, don't know if many local spa shops would keep them in stock, may have to get it ordered ....
Good luck

Thanks for the advice.... and I have good news!

I emailed the company (United Spas) and they agreed with your analysis. They offered to send me a vacuum switch to replace the pressure switch. These guys have been top notch in terms of customer service. I'm very impressed and would highly recommend them.

one final note...

I checked the switch with my multimeter (with the system power and the switch connectors disconnected) and determined that bypassing the switch by hotwiring it wouldn't cause any damage. I used a pair of plyers to pull up on the pressure switch plunger and close the circuit on the switch and measured the resistance, then checked the resistance across the connectors on the switch by shorting it with a screwdriver. The resistance when the switch was activated = resistance when bypassing it.

The heater now works (and shuts off) perfectly with no FLO error message.

NOTE THAT I'M ONLY DOING THIS AS A TEMPORARY FIX WHILE I WAIT FOR THE VACUUM SWITCH TO ARRIVE FROM THE MANUFACTURER.

crude..... but effective

glad to hear they're providing you w/ a vacuum switch, and offered great customer service...

~Enjoy