Power Steering Issue

My car has EPS. The Power Steering Failure would illuminate and steering is difficult. Turn off and on car, power steering was restored. Now I have a hard failure of the power steering, but randomly when you start the car, the power steering works for a limited amount of time. No diagnostic codes are generated. I took it to an auto shop, they see a thermal error, but they do not believe that it is a power steering column or motor issue and I disagree. Any suggestions? I would rather not replace both the steering column and motor, trying to determine what is actually failing.