I purchased a house with an inground 20 person spa. After opening it up this year a I discovered a problem with the jets. When I turn on the jets water flows out of one of the air intake tubes. Any idea what the cause is?

Loose inner jet fitting, or "eyeball"

Just tighten all the jet's, and if that doesn't do it, replace the innards. (No draining needed, they usually just screw in)

I'm having the same problem on a 4 person spa. Water was being pumped in to the air induction system. An air line popped off a coupling and water started leaking everywhere. Like an idiot I drained the tub before I had a chance to verify what jet was causing the problem. I replaced mini WaterWay jet that looked broken. Haven't had a chance to refill the water and test. I do have a question on the whole air induction system. How is it that water does not fill into the air lines when the tub is not running, or does water fill air lines until it reaches the water level? I understand the venturi for pulling air into the tub, I just don't see how water will not flow into the air lines tubs when the tub is idle.

Any help appreciated. Thanks

Water will seek it's own level. There's usually a check valve as well, or the AFC is above the water level, or both. If the AFC is below water level, and there's no check valve, water will just pour out with the pump off.

There is no check valve. Not sure what AFC is short for. It looks like the air induction manifold is below water line and a few of the air lines will likely flow back into it. Some of them go from the jet up above the water level. Have not had a chance to fill it the tub yet. When the pump is running and the air knob is set open the venturi effect should pull the water out of air lines, and air should start flowing in as well?

Thanks for the help. I really appreciate it.