The rectangular white antenna is indeed the Zigbee antenna. Someone suggested to me once that I replace it, and I've loved it ever since I did. 
Here are the instructions I used:
I chose the flat "leaf" antenna because that poster said it may have been slightly better.
Before I did this, I had lots of problems, widely reported with these units. It was hard to pair unless the hub was extremely close (same room; 10 ft might be OK). Repeaters nearby (you usually see one or two in the same room suggested, or possibly the room above) are pretty much essential to keep it from "falling off" the network otherwise. With the new antenna, I moved my repeater to the other room where I really wanted it, and then it paired through the mesh (I assume--at the very least, the hub was fine where it was) just fine and didn't fall off since.
But since you have it like this already: my advice would be to keep the hub close, keep a Zigbee repeater close, and keep trying. The reset procedure also seems to be a bit picky about how many seconds you keep it on/off (I forget what the exact recommendation is and what I tried that actually worked, but try again if your first attempt fails). They're probably still tricky, but I think the antenna/weak signal is a big part of this. You shouldn't need to turn it off at the breaker unless your switch doesn't control the entirely of power to your fan/unit, but that would be about the only way to perform the reset procedure if yours doesn't for some reason.
Good luck!