Forget the check valves, they are not there. They are air venturri lines that supply air intake to the WATER jets. That is what gives you the air water mix. The motion of moving water pulls air into the jet stream by venturri action.
Sit against the jet and block the water from coming out, well guess where it goes. Cover your mouth with water coming out and the water comes out your nose. Nothing is wrong here. Run the jets and open the air venturri's to clear them of any water. It is a natural action.
If you block the water from coming out of the jets, or the ozone inlet, it only puts back pressure on the water to seek an altenative route. It is possible to start a venturri syphon draining action that will drain the spa until the water level drops to the level of the air intake, then it will stop. Again, no problem here either.
Cancell the service call, it is not covered under warranty.