A Zigbee network is only as good as its routers. The coordinator can only hold a limited number of direct children (the Zigbee2MQTT FAQ documents 20 for the old CC2531), and every router both extends range and adds capacity.
Procedure
- Place the coordinator well first: USB extension cable, USB 2 port, away from SSDs and Wi-Fi.
- Add routers before end devices. Mains-powered devices that route (many plugs, bulbs, in-wall switches) or a dedicated router (Zigbee2MQTT mentions e.g. a SONOFF ZBDongle-E based router). Spread them so every room has one.
- Pair battery devices at their final location (or next to the router they should use), not on the desk next to the coordinator. An end device keeps talking through the parent it picked.
- For devices that are picky about routers, pair through a specific router (Zigbee2MQTT supports permitting join via one router; it mentions Aqara devices as an example).
- Leave routers powered. Switching off a smart plug or a bulb at the wall takes its children offline until they find a new parent, and some devices never do.
- Check the network map and link quality after changes; re-pair isolated devices near a router.
Know your end devices
- When a parent goes offline, its children are unreachable until they time out and search again.
- Some end devices (Zigbee2MQTT names Xiaomi) don't search for a new parent at all and stay isolated until re-paired.
- Sleepy end devices may disappear from a router's child table and still work: the Zigbee2MQTT FAQ notes a missing network-map link doesn't necessarily mean the device is disconnected.
Signs you need more routers
Devices far from the coordinator drop off, pairing only works in some rooms, commands arrive with delay: add a router between them before replacing anything else.