hotpoint dishwasher bf1680?

i have had a service man to look at my dishwasher and he says something is staying open at the bottom of the dishwasher stopping it from starting.no lights are on and the overflow pump runs all the time.i have a wonderfull father in law who is a qualified electrician and fork truck engineer who i am sure could change the part if i knew which one it is.the service man said it would cost around £150 to repair but in this current climate there are far more important things to spend money on with 3 young children can you help me find out what i need many thanks for your help