Washer fills....and keeps on filling....flooding my house?

My son recently purchased a second hand washer and dryer (Whirlpool Thin Twin). We were assured this was a fairly new set, no more than a year old. He came home the other day to find the entire back part of his house under water. The washer apparently filled and did not cut off. What parts are needed to fix this? Sorry, but don't have the model no. at this time. If needed, I will send it. Just talked to my son on the phone but he is not at home at present.