This applies only to snap-in jet inserts. Beginning with 2013, new spas use jet inserts that screw in and are unlikely to pop out
Some jet inserts are designed to rotate about a half a turn in order to turn on or off water flow. They are also designed to come out if you turn them past the attachment. When a jet insert is turned past its attachment point, it can be easily blown out of the jet body with water pressure. To prevent this, rotate the jet insert only as far as it will easily turn until it hits the stopping point.
A jet that keeps popping out may not be pushed in all the way. By pushing in on the jet insert, you should hear a click. This indicates that the insert is installed all the way into position. If there is no click, the jet is in the wrong way and will pop out.
Sometimes jet inserts weaken over time due to constant exposure to water and chemicals. If the jets are subjected to extreme chemicalconditions or abuse, they will weaken and fail.
If the jet insert is a replacement, if it is the wrong size or type for the jet body, it will not stay in place. Change the insert to the correct size or type. Many inserts look alike and have the same size face. The nozzle in the back is where the clips are located and is what has to match the jet body.