It is aligned correctly...with the pumps both on and off, it reads 00.0 (no resistance?) With the breaker shut off, I get a reading in the mid 16.0's

...also, as I understand it, the ozone air pump is what creates the circulation for the heater to work, so it would make sense that the flow switch wouldn't have any resistance whether the main pumps are on or off. Is that correct?

Regarding the jets being on, that depends on how it is plumbed. Some circ pumps have their own dedicated suction, others are fed through the jet plumbing. When the tub was heating before was that only with the jets on?

No...it heated without the jets on.

Hmmm. Let's go over all this again.

FLO1 = No water flow detected when the pump is on and heat is called for.
FLO2 = Water flow detected when the pump is off and no heat required.

If you turn the spa off, jump the terminals on the board for the switch, and turn back on you get a FLO2 as is normal.
If you turn the spa on with the switch disconnected, wait for the circ pump to kick on and FLO1 to appear, and then jump the terminals, FLO1 goes away and you get heat.
With the spa on and both jets off but the circ pump on, you get 0.0 continuity reading. With the spa off you get somewhere around 16.0 (should go to OL, but if that was an issue you'd be getting FLO2).

Is all that right?

Where are you testing continuity for the switch? At the plug? If you're getting 0.0 at the plug, then plugging it in should be as good as jumping the terminals so a good first step would be to turn the spa on with the switch unplugged, wait for FLO1 to appear, and then plug it in.

Correct on everything...I did try turning spa off then on, and the when the jets kicked on I plugged in the flow switch but the flo1 stayed on.

I am testing at the back of the plug ....the plug that connects to the board...there are exposed wires there.

I don't know why I would get a different result from jumping the terminals than I get from connecting the flow switch but that's what's happening. I would think I'd get an OL or at least some numbers if there was a problem with the wiring or connection. I'll check my results again.

I also hooked up another air pump (an aquarium air pump) just in case the spa air pump wasn't putting out enough air to circulate the water.

There's also a question now if it's actually heating. It indicates that it is, but it doesn't seem to be putting out warm water.

here's a link to a post from someone awile back and about halfway down is a diagram that seems to illustrate my system pretty well.
(I couldn't figure out how to post just the image)

Spa-Repair/Digital-Spa-Pack/Dimension-California-Ultra-Crystal-Pure-Balboa_153.html

When you say it indicates that it's heating, you mean with the terminals jumped?

Very interesting system. I've never had the pleasure of working on one. Since your flow switch is (apparently) closing, I'll assume all is ok with the air pump. Are you seeing bubbles as described in the other thread?

Did the new flow switch come complete with a new cord and plug or did you have to use your old one? Double check your results, but if they're right and jumping the terminal makes the error go away, we're not left with much other than a loose connection with the plug.

Yes...with the terminals jumped,I get no error message and the display indicates the system is heating. I am getting the bubbles described (with the aquarium pump) .....and I did have to splice the old plug onto the new switch. Is it possible something happened to the heater due to jumping the terminals?

Check the resistance on the heater. Should be between 10-15 ohms. If it reads OL, check to see if there's a high limit reset on the heater itself. Running the heater with the terminals jumped could harm the heater or trip the high limit if there was no circulation.

Take a close look at the plug itself. Maybe even "plug it in" to two separate wires and check continuity across them instead of at the plug itself. Sometimes wires will jiggle loose from the barbs on the plug that pinch in and actually touch the conductor part of the wire.

I just re-tested the flow switch and with it unplugged and taking readings from the front of the plug and at the splice, I get 00.0 on the meter. Then I cut the plug off, tested each side and tested both terminals with each wire end. Got 00.0 for both matching wire end/plug terminal and got OL when I cross-checked each terminal with the other wire end. I got the same 00.0 reading when I checked the flow switch from the bare wire ends.
The heater tested at just over 15 (15.2).
The flow switch appears to be working except when I connect it to the board (???)
I'm stumped.....