Short answer: a router that restarts by itself usually has one of four causes: the power supply, overheating, outdated firmware, or a scheduled auto-reboot setting. Check them in that order. Each one is free to check.
1. Power
A flaky outlet or the wrong adapter causes repeated restarts. TP-Link and NETGEAR both recommend trying a different outlet and using the power adapter that came in the box, and NETGEAR also suggests a UPS (battery backup) to ride out power blips. If you’ve swapped adapters at some point, check that the voltage on the adapter matches the label on the router.
2. Heat
Routers need airflow. TP-Link advises against putting the router in a cabinet, on top of other electronics or near heat sources, and NETGEAR notes that small spaces can cause overheating. TP-Link also points out that enclosed spots trap heat and block the Wi-Fi signal. Moving the router into the open often fixes both problems; see where to put your router.
3. A scheduled auto reboot
Some routers can restart on a schedule. TP-Link says this setting is sometimes on by default, and is easily mistaken for a hardware fault. If the restarts happen at the same time every day, look for a reboot schedule in the router’s system settings.
4. Firmware, then a reset
Both TP-Link and NETGEAR recommend updating the firmware, and if that doesn’t help, resetting to factory defaults. See how to update your router firmware. A reset erases your settings, so note your Wi-Fi name and password first.
Could it be compromised?
Occasionally, odd behaviour is a security problem. The FBI lists overheating, connectivity problems and settings changes you don’t recognise as possible signs of a compromised router, and recommends replacing routers that no longer get updates. If you see unexpected settings, update the firmware, change the admin password and turn off remote management; our router security checklist has the steps.
If your router no longer gets firmware updates, it’s time for a new one: see when to replace your router. If only Wi-Fi drops while the router stays on, see why Wi-Fi keeps disconnecting.