Jouan B4i centrifugue

Please can anybody help me, our B4i Jouan centrifugue shows "Err" in the 2a display and the number "8" in the 3a display, right wen it started to run, some times reach 500 rpm some times 800 rpm or some times don't even start.

There is no information about erro codes in the user manual.

Thankd in advance

Alfredo