Elevated spa drains into pool.

The heater causes a lot of flow restrictions, there are plenty of threads here on heater bypass and their performance results. The most ideal setup to get the most out of your jets would be, having a closed loop intake>jetpump>jets without going through the heater or filter(this needs to be planned during build process). You only have one intake for the spa and return to spa is either jets or spa wf. It wasn’t designed for an additional jet pump. I think a 3hp vs and the setup drawn above will perform just as good or better. It will simplify the system making it easier to automate in the future.
 
Success \o/ The spa water is no longer draining into the pool when both pumps are off (drawing attached) - not even a fraction of an inch. I had to:
1) Replace the internal flapper assemblies of all 3 checkvalves with authentic Jandy replacements. The generic ATIE versions did not fully seal. Check valve #1 (after the filter) was *completely* busted - plastic had worn away, the spring had no tension (it was just flapping), dried glue on the inside of the pipe, etc. Picture attached.
2) Replace the internals of the Pentair 3 way diverter valve V-3. After many years, this part seemed worn away and probably wasn't holding a great seal (picture attached). There was also some dried glue I had to remove with sand paper.
3) Replaced the NSI Tork Actuator on V-3 with a new Pentair actuator. I suspect it wasn't closing all the way, and it was quite old. Perhaps I could have adjusted the internals but I instead just purchased a Pentair actuator that I figured would be designed to better work with the Pentair diverter valve it sits on top of.

Thanks so much @Jimrahbe & @Poolbreh for the insight about the problematic plumbing & multi-pump design that I inherited. I will be installing a Black & Decker 3HP VSP over the coming weekends and I'll seriously consider replumbing to one of the single pump designs as suggested by @Poolbreh once I feel more confident in my pool/PVC/plumbing skills.

You all rock. I've joined as a Gold Supporter in appreciation of you valuable people and this valuable forum. Thanks again!
 

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Quick update: I installed the Black+Decker 3HP VSP and it is able to power the spa jets, no problem.

I leave the pump running 24x7 (at 1500 RPM) because it's very cheap.

I re-plumed the pool as per the drawing from @Poolbreh in #18 but when the pump is off the (higher water level) spa drain drains back into the pool drain because there's no check valve on the pool drain/skimmer :/ Oh well - this is not a huge deal for me any more because (1) I know how to fix it if I so desire (2) the pool runs 24x7 now that I have a VSP. The spa draining into the pool was a major issue when I had a 2 speed pump (stuck at the highest RPMS...) and therefore turned it off every night - but that's not the case anymore thanks to the 24x7 running of the VSP.

This thread can be closed - thanks to everyone who helped - especially @Jimrahbe and @Poolbreh
 
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