The fan won't do much if there's no heat in the room.
Notice the two doors on either side of the chamber. Lava comes in through the left door and exits to the right. Knowing this, how can you make sure lava will be in the room when you leave?
Be sure to leave the gear on the left side of the room when you exit. Then, use the controls in the windowed room to raise the lava door (and platform). You're ready to move on once lava has entered the chamber.
