Hello
This is your foot valve that is bad
The foot valve is in the bottom of the well inside the suction pipe that goes to the pump
This valve lets water go in one direction and not the other
Yours is letting it go back into the well
The good news is you can install a check valve on the pipe before the pump
This will act as a foot valve however it may cause the pump to loose it's prime
It wouldn't hurt to give it a try before pulling up the pipe going into the well
I hope this helps if not let me know.If it did please click the {Green}accept button
A bonus is always nice and don't forget to leave feed back
thanks Glenn