WM61, Why does my washing machine keep filling with water and won't stop?

Thanks JP for your answer,i should have said that the machine fills with water when turned on a fill cycle as it should but instead of turning off when the correct amount of water is in the drum it continues to fill until it over flows.if i turn it onto a empty and spin cycle this function still works. do you know if theres a timer which controls the amount of water going into the drum or is there a sensor which turns the water off when it has the correct amount.