Pressure Switch!
I don't know if you can buy one separately or not.
My old Aqua Jet just needs a few pieces but I have to send it to them/ 69.00 plus 69.00 shipping. So bought new one at Rally from factory for 149.00 and they put it in.
Ours did a little differently. It wouldn't shut off but no water until you cut the wter pump off and back on and you had water. Tun the faucet off and it still ran a bit of water but not much then none. Check valve and switch I think but they won't sell me the parts. I may pull it apart and see if it is just debris or something and keep it for a spare. Just make sure if someone else installs it they don't lose the screws to the cover plate and try to use wood screws. Amazing how hard it was to find stainless screws an had to substitute stainless cap screws.