miele novotronic w715 how to repair?

My washing machine fills up and then tries to start washing but the door keeps popping open and the program won't continue. I thought it was a faulty lock so wedged it shut until we could get another to repair. No matter what we tried it will not stay shut and opens itself.Almost as if it is a safety thing. Have had the machine for many many years and so far this is the only problem so if possible want to try and repair DIY rather than MIELE as can't afford their repair charges.