When an S21, S21+ or S21 Ultra will not connect to Wi-Fi or keeps dropping it, work through Samsung's list: restart, update, confirm Wi-Fi is on, forget the network and rejoin, then test in Safe mode. After that reset Wi-Fi and Bluetooth settings and check the router. There is a real hardware split here: Wikipedia lists Wi-Fi 6 on the S21 and S21+ but Wi-Fi 6E on the S21 Ultra, so only the Ultra can use a 6 GHz network. The Ultra also has Bluetooth 5.2 against 5.0 on the others.
Differential
Likely causes of “Samsung Galaxy S21 family will not connect to Wi-Fi or keeps disconnecting”, and how to tell them apart
- 1
A software glitch
What separates it Wi-Fi fails after a long uptime or update because of a software glitch
How to confirm Restart; hold Side and Volume down over 7 seconds if frozen
- 2
A saved network gone bad
What separates it It sees the network but will not join or has no internet
How to confirm Forget it and add it again, with the right password
- 3
A recent app
What separates it It works in Safe mode only because of a recently installed app
How to confirm Remove recent apps one at a time, and test Wi-Fi each time
- 4
The router
What separates it Other devices on the same network fail too, so the router or internet service is the likely cause
How to confirm Update the firmware and power cycle the router, then reconnect
- 5
A 6 GHz-only network
What separates it The S21 or S21+ cannot see it because it is a 6 GHz only network
How to confirm Wikipedia lists 6 GHz only on the Ultra; enable a 5 GHz name
Before you touch a setting
Record this first — changing settings destroys the evidence
- S21, S21+ or S21 Ultra and the software version
- Whether other devices and networks work, and the band
- The router make, model and firmware
Try in this order
0 of 7 completedRestart
ReversibleRestart, by using the power menu, or Side plus Volume down for over 7 seconds.
Update
ReversibleOpen Settings, Software update and install anything waiting, then restart the phone and see whether the fault has cleared.
Forget and rejoin
ReversibleForget and rejoin, by long pressing the network in Wi-Fi settings and choosing Forget, then joining again.
Safe mode
ReversibleTest in Safe mode, by long pressing Power off, and if Wi-Fi works, remove recent apps one at a time.
Router
ReversibleCheck the router, by updating the firmware, checking other devices and power cycling the router.
Reset network settings
ReversibleReset network settings, by opening Settings, General management, Reset, then Reset Wi-Fi and Bluetooth settings.
Radio test
ReversibleRun the radio test, in Samsung Members, Support, Wi-Fi test, and book service if it reports a fault.
Model-specific
What is true of this model and not of its siblings
- Wi-Fi and Bluetooth
- Wi-Fi 6 on the S21 and S21+, Wi-Fi 6E on the S21 Ultra; Bluetooth 5.0 versus 5.2, per Wikipedia. The S21+ and Ultra add Ultra Wideband.
- Chips by region
- Snapdragon 888 or Exynos 2100; Samsung's Wi-Fi article treats all three alike.
- Part numbers
- Record the router's model. There is no phone part number involved; the SM- model number is under About phone.
- Tools and supplies
- A second device, the router admin page and a flashlight for the router label.
- Repair cost
- Wi-Fi faults are rarely paid repairs; a faulty radio is quoted by Samsung. US screen-only prices are $174, $199, $229.
Stop boundary
When this stops being a self-service repair
- !If it fails everywhere after a reset and diagnostics, visit a Samsung center
- !If it drops beside a good router even in Safe mode, book a radio check
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Which S21 has Wi-Fi 6E?+
Only the S21 Ultra, per Wikipedia; the S21 and S21+ have Wi-Fi 6.
Bluetooth version?+
5.2 on the Ultra and 5.0 on the S21 and S21+.
How do I reset settings?+
Settings, General management, Reset, Reset Wi-Fi and Bluetooth settings.
What does Safe mode show?+
If Wi-Fi works there, a recent app is the cause.
Will photos be lost?+
No, resetting network settings does not delete your photos or other files.
What does connected with no internet mean?+
The phone joined the router, but the router has no working route to the internet, or a setting such as private DNS or a VPN is blocking it. Test another device on the same network; if that fails too, restart the modem and router in that order and check for a provider outage.
Will resetting the router help?+
Restarting it often does, and is the first router step. A full factory reset erases its settings and passwords and should be a last resort, done only if you know the login and setup details, because the router's maker is the right contact for that.
Does the S21 support the 2.4 and 5 GHz bands?+
Yes. All three models support the usual bands, and the Ultra adds 6 GHz through Wi-Fi 6E. If a router broadcasts one name for both bands, splitting them into separate names lets you choose the band on the phone, which often fixes a phone that clings to a weak 2.4 GHz signal.
Do I need to reset the phone if Wi-Fi keeps failing?+
Rarely. Samsung's order puts a restart, an update, forgetting the network, Safe mode and a network settings reset well ahead of a factory reset. Work through those first, and only consider a full reset, after backing up, if the Samsung Members Wi-Fi test still reports a problem.