So I've noticed in a few rare occasions that sometimes I stumble upon a dps in a dungeon who I have a hard time with to fully heal up. As a Templar, when I use my main burst heal, normally I get a person's health to 100%. But sometimes there is a dps and when they lose health, I use my burst over and over again on them and it hardly seems to have any effect on them. I am just wondering what this reason could be. It doesn't happen a lot, but I am just curious. It can be a little frustrating not being able to keep someone at full health.
Extra info: I am a Breton Templar, CP 520 and wearing both Spell Power Cure and Hollowfang sets.