[newheart]

Has anyone actually read his book? Has he really claimed that there is no hell?

Yes. And no, he didn't.

[Lakeshark]

If he didn't say that there was no Hell, what did he say and why did he get dumped by Mars Hill?

The fact he said a few things that deeply disturbed the people of his congregation (who quite clearly once loved his teaching) enough to get rid of him implies it must have been pretty far from or contradictory of the New Testament teaching.