If it has the problem with only the one tank, it is the tank that is the problem and replacing the device will not solve the problem. Since you have tried several heads, it is likely not to be a shorting problem, but rather a connection problem between the head and the pin in the airflow controller or between the pin of the airflow controller and the firing pin of the device.
I would first remove the airflow controller (the base of the subtank mini), thoroughly wash and dry it, blowing into it from the top to blow out any excess moisture. Before replacing the head, make sure that the bottom is completely clean and free of any dirt or gunk. Also, make sure to screw the head back into the base firmly to ensure it is in all the way.
If this does not solve the problem, you can also try to push the pin of the airflow controller out just a little bit. The handle of the blue screwdriver that came with your subtank should be the perfect size for this. Do not push the pin out too far--just enough that it is sticking out beyond the threads of the 510 connector. Then replace the head and try again.