It will start repeating right away, you don’t have to do anything for that. The issue is does it know which neighbors it should be repeating for? And do those neighbors know about it?
There are two possible situations.
A) you plugged the device in to the place where it will remain. Then you paired it. At the time of pairing, it took note of all the devices that were close to it. So the repeater’s neighbor tables are all up-to-date.
(Each device on the mesh network keeps A list of the neighbors closest to it.)
The problem is that those neighbors don’t necessarily know that the new repeater even exists. So it’s a good idea to get them to update their neighbor tables. That’s why you need to do either a network heal for zigbee or A zwave repair for Z wave. Then everybody’s neighbor tables will be up-to-date and messages will be passed around in an efficient manner.
Or B) you plug the new Device in close to the hub. You paired it. You then unplugged it and walked it over to some other place in your house and plugged it in there.
Now we have two problems. The new repeater has no idea who its real neighbors are. And the neighbors have no idea that it exists.
The solution is exactly the same as for A) – just get everybody to bring their neighbor tables up to date. So you do a network heal for zigbee, or a zwave repair for zwave.
Basically anytime you’re adding new mesh devices to your network, whether they’re repeaters or not, once you have paired everybody and put them in their final locations, you should get all the neighbor tables updated.
It’s easy. See the range FAQ: