Why is my transistor getting very hot when controlling a 12V peristalic pump?
Measure the Current through the motor, the PN2222 can pass a maximum of 600mA.
I would guess that just over half an amp would be enough for the motor but you can check what you motor is trying to pull by connecting it to 12 V direct and measure the supply current.
The only thing that will make the transistor hot is excess current