If the controller works fine with another fan, it doesn't seem likely it is the controller. Did you check the wiring on the big fan?
Ah, well, there's nothing in any fan that can make it spin when there is no power applied to it, and when the HM has the blower speed set to 0% there should be no power applied to the blower if things are working right... So the problem isn't the blower, it's gotta be either your CAT5 wiring is wrong or the HM has problems.....