Did this last night for the first time. We wiped initially on the last boss, due to too many taking fire damage. We also suffered from the bug where you catch fire, just standing at the entrance to the room before pulling the boss, but that stopped when we entered and stood in a corner of the room.
We eventually killed him on our 5th attempt, just by good observation and group movement. Fighting him in the corner of the "safe" quadrant, helped considerably.