I have a Jandy system and when I turn the pump off the water from the jacuzzi is going into the pool.

go to system set up see if programs if you have a 4 button spa remote disconnect and see if it goes away sometimes they get water in the wiring no programs are stored in the PDA

That is because the return line to the spa and pool are on. This is expected behavior. This is to keep water circulating.

go to system setup see aquapure turn chlorine production 5% or more and you should see it on the menu

This is an ether or situation. Most systems now are set up with three way valves and if you turn the jets on you will shut the pool returns down. If you turn the pool back on you will shut the spa jets off.

you probably have a check valve (back flow preventer) on the line that supplies water to the spa when the pool is filtering as normal. Your check valve may have some debris in it or the seal inside may have failed allowing the water to drain into the pool when the system is off. You should see a valve on the return line that splits off from the pool return line on your system. There are several different check valves on the market, some have a clear lid that you can inspect without taking it apart. Some of them cannot be taken apart. Your challenge will be to find the check valve, then try to check to see it debris may be holding it partly open or it the rubber seal inside is damaged or missing. I hope this helps.

make sure pool is full of water
check skimmer weir doors and make sure not stuck in up position
fill pump basket with water and try to prime

if that doesn't work

replace diffuser oring

http://www.jandy-downloads.com/pdfs/PHP_Manual.pdf

I agree it sounds like a check valve. if the water in the pool matches the water level in the spa, or drains all the way (depending on how far the spa is raised) then it is the valve before the pump, but if it goes down to the jets (and not any further) then it is a check valve or valve on the retun side of the plumbing ( after heater or chlorinator).

This is nothing to be concerned about, manually shut off the pump and watch for water leaking somewhere and fix

You need a new impeller kit. Does any one know where to find one?