Burned: Dragons' Trust Book 2 by Krista Wayment

Renick, apprentice dragonhand, discovers that nothing can stand in the way of a dragon’s thirst for revenge. Caught between an outcast dragon and his human prey, Renick and his friends must find a way to appease the dragon’s burning anger. Together, Renick, Thane and Lainey learn new magic, rescue a kidnapped friend, and evade the dragon hunters while the try to prevent a war. What they find is that not all burns can be healed.