Well; looking at the manual is seems that the red LED indicates a problem with either the radial blower or the separation system.
Just a guess ... but I would look closely at the separation system in the first case, and the blower in the second. Either way I would disconnect the separation system(s) and try again.
But two machines? From the same user? What story is the user giving?
I'm putting my money on flooded ... blocked ... dirty ... separation units (but hopefully not as far as the blower) - most likely due to "operator error" or lack of cleaning etc. Let's see if I'm right.
I wonder what cleansing agent(s) are being used. I should imagine that Dürr are pretty fussy in their requirements.
