There is usually a water level sensor, in the way of a pressure sensor. I have found that some time the pipe blocks. You would need to open up the machine to sort it. The level sensor is about 3" diameter, connected via a pipe, down to the drum, the pipe does clog up, due to the soap. you would need to find that and clear the pipe. That is the first thing to check. After that, yes possibly control unit
SD, July 2011