Vivi Mini Nova Question...

[heroinesick]

How do I know if I need to replace the head? I generally rinse and dry burn it once a day at least. I've got an extra bunch of heads and stuff, and I know they can last anywhere from 5-12 days. But how do you know it's time to change it out?

Thanks in advance!

 

[heater]

I notice a tighter draw.