This Gecko spa heater is specifically for the YJ spa pack as it has the flow sensor and the temperature sensor built in to the heater for the YJ spa pack as well as the cord to connect the heater to the circuit board.
 
Details:
4.0KW, 230 Volts
With Flow Sensor and Temperature Probe
Includes Stainless Steel Housing, Heater Element and Split Nuts.
Includes 4' Cables to plug into IN.YJ Control Pack
For IN.YJ Gecko spa control pack