Fire is a element of nature, that can be used to kill vampires by burning them.
Because a vampires skin is extremely sensitive to heat, and like with sunlight, long exposure to fire will permanently kill a vampire. Fire is a destructive force that the undead are vulnerable to, so if a vampire is exposed to fire for a prolonged period, they will be reduced to ashes.
Theo Quinn: Theo cannot be killed by burning, but still brings him excruciating pain and discomfort. His healing factor will heal the burns when he stops burning.