Sion W passive doesn't work [gameplay]

Hi guys, i was playing ranked 5v5 solo queue and picked Sion top. I took q first, then w. But, when i killed several minions i noticed that i didn't get any HP bonus, which i should have gotten with w passive. Then i died, and after that i killed my top enemy(rengar). But even after that still no bonus health. Then i quit and reconnected and killed more minions and champions but my health bonus stayed 0. Even in the end, it stayed the same. I finished the game with 0 max health bonus. I hope that you can fix this.