Power steering failure

Recent problems with failure of power steering whilst driving.  This was dangerous as I don't have the strength to turn the wheel without the power steering.  Nobody told me that, if the power steering goes, all you need to do is stop and turn the engine off.  When you restart it, it resets the power steering.  However, problem persisted.  AA recommended a new battery.  I had this put in.  Problem persisted.  First garage said they thought it was a problem with the steering rack.  I looked for this part, but almost impossible to find for a 2009 Mark 111 model.  Second garage said that they had put it through the diagnostic computer check and the only fault showing was the Torque Control.  This was confirmed to be on the steering rack.  I was facing a huge bill for the new steering rack - IF it could be found!  Driving the car, I suddenly found the fault had ceased.  Still unsure, I had a good chat with the service manager at yet another garage today.  He explained that the 'fault' code can be activated if, on one occasion, the torque control fails to supply the necessary assistance to the force the driver is applying for steering.  To reset, you not only need a new battery, but you need the car completely 'shut down' which happened when it went through the diagnostics.  The combination of the two has now shut down the fault code, and I shall not need a new steering rack.  The lesson I have learnt is, keep your battery up to date for all things electric.  Hope this helps some of you.