Discs should be rotating all the time as you have been advised. Possible though if the unit has been stationary for some time, the discs are unbalanced, i.e. the bottom half are heavier as they've been sitting in water, so the motor is struggling to provide the required starting torque, and thus blowing something.
If power is getting to the unit, it's maybe worth removing the drive belt and checking if the discs rotate freely before doing anything else. These units usually have grease points on the bearings, if these are dry, it may be struggling to rotate, hence your issues. They are heavier than you think, seen one lifted one out of a larger version that serves a small village. The engineer estimated 7 tonnes. Crane was rated to lift 12 tonnes, and wasn't happy, driver estimated he'd got around 11 on the hook!