A PP.
Here is a thread with the beginnings of a diagnostic routine.
https://www.reddit.com/r/Appliances/comments/1faffp3/dishwasher_not_getting_water/
Comment by Shadrixian:
"Alright. Lets start from the very beginning. Lets look at what all we have. A sink, a dishwasher. Do we have a garbage disposal? Keep that mind mind, yes or no, and lets move on.
Start a cycle. Let it sit for a minute, then open the door and shut it. Now hold the start button until it cancels. Does the pump run?
Next, start the cycle, but get down close to the bottom left. If the valve is running with no water to it, it will buzz. If there is water, youll hear muffled trickling, kind of like a hissing or spitting sound. That means water is getting into the machine. If it doesn't, it could be as simple as a chewed up wire.
Now, assuming that it filled, if you pull the spray arm off and take the filter out, there should be water in the sump. Is there any?
Now lets experiment. Get a pitcher. Fill it with water, and pour it in. You want just enoigh to sort of cover the bottom, but not enough to trip overflow. See if it washes.
Next, cancel. Drain it. Does the pump run? Can you hear the sink drain gurgle? Lets look under the sink. Does the drain hose have an upward loop before it connects?
And remember the garbage disposal question? If water didnt drain, and you have a disposal, take the hose off, stick your finger in the hole(it wont eat you unless the switch is flipped). Youre feeling for a cap or plate, thats a knockout and is meant to be removed before hooking dishwashers up.
Let me know what you come up with, and I'll know where to lead you next."