I’ve had my Aspire CF VV for about 8 months. It’s been working great but lately I have been having trouble pulling vape. I press the button and the light goes on. I hear it working but I have to suck very hard at least 7-8 times before I hear it open up and vape smoke gets sucked in my mouth. I’ve tried multiple cartridges and they all do the same. Is there something I’m not doing properly ?