1) Take the shaver out.
2) Unplug the Jet Clean System.
3) Clean the level sensors (the tiny metal parts at the end of the 2 plastic teeth) with a cloth. (fig. 1, indicated with the green arrow)
Note: your Jet Clean System may look different from the one in the pictures.
4) Plug the Jet Clean System back in.
5) Place the shaver upside down in the holder and push the lever down completely to lock the shaver into place.