Model Number: WDF750SAYW2
Brand: Whirlpool
Age: 1-5 years

My dishwasher fills with water. Then, when the wash motor should start, nothing happens.

If I leave it alone, the dishwasher will drain and refill the water at the appropriate times, until the cycle completes. But, in between, the wash motor won't run.

I learned to do this:
1. Begin the wash cycle. (It doesn't matter which setting I use . . . "Sensor," "1-Hour Wash," etc.)
2. After the water finishes filling and the motor doesn't start, I press "cancel".
3. The water drains, then the dishwasher turns off.
4. I begin another wash cycle.
5. About every 4th or 5th time, the wash motor engages as it should, and the dishwasher completes its cycle normally. It washes the dishes fine.

How should I troubleshoot this?