My head system is inoperative. There is no vacuum at the head but my vacuum generator is producing vacuum showing a green light, ready to flush. I proved vacuum at the vg2 by pulling the vacuum switch out which turns the pump on and then will build vacuum again when the switch is replaced shutting down as expected. For that reason I feel the duck bills are ok, am I correct in assuming that? There is no visible clog at the head. What would you check next?