If you're at the point where you can control the flame cap, then kill all the fire bots immediately. If you're not at that point, don't kill any of them. They can end up putting out almost the entire room.
Our holy paladin made a video that, aside from having an annoying UI, displays our positioning and the effect it has. Phase 1, melee runs in the middle, ranged to... well, one area, but spread out. Tank pulls the boss towards a door as fire creeps up, gets the boss to the door before the phase 1 extinguish, ranged repositions behind the tank (in the boss kite path), still spread out. Blah blah, it's shown pretty well. You'll see a solid wave of fire against the back wall as a result of this.
In phase 2, the previous fire will be almost completely put out. Now you just have your ranged hang out together and make sure that your melee are not between the boss and the ranged (causing everyone to take the hand blast).
In our video, you'll see that, while we handled the magnetic cores sloppily (using them too close to a new fire spawn), there are never any real fire hazards that we face. And for 3/4ths of phase 4, there is literally no fire -- the bots put it out immediately. Of course, you have to run away from new fire spawns to not get blasted by water, but that's not hard at all. Our entire phase 4 would've been devoid of water, had we not killed the bots through incidental damage.
It's in two parts. Make sure to view them in HD.
http://www.youtube.com/watch?v=LBmj8EUn ... re=relatedhttp://www.youtube.com/watch?v=E0SqvYNu ... re=related(This isn't necessarily the best way to kill the boss, but it works for us... in fact, it works pretty well. I hope it helps.)