Hi Fer Kix
No you do not need to replace your machine, but we do need to have some more information before we can tell you what to do.
The question is does water come into you machine regardless of whether or not it is turned on, that is, when you open the valves to let hot and cold water into the machine, does it come into the machine even though you have not pulled out the control knob? In this situation the way of course you have to stop the water is to turn off the faucets.
Alternatively, does water continue into the tub only after you have started the machine, and the water does not stop unless you push in the control knob?
Also, does this happen with both hot and cold?
Just so you know, the way the water level works in your machine is that there is an air pressure switch which is activated by air trapped in a plastic tube. As the tub fills, pressure builds and when it reaches a certain point the water level switch is engaged and tells the timer the tub is filled. The timer then shuts off the inlet valves and starts to wash your clothes. If water comes on even if the machine is off, the problem is in your inlet valves, an easy fix. If water shuts off when you shut off the machine the problem is probably in your water level system, also an easy fix. Finally, the problem could be in the timer, which is unlikely. This is an easy, but more expensive fix.
Anyway, post the info and let's see what we have.