How to set up automatic broadband failover at home, step by step

This guide covers all three routes, then the parts that apply to every setup: detection settings, testing, power cuts, data use and troubleshooting. Menu names are given for TP-Link equipment where the manufacturer documents them; other brands use different labels for the same ideas. Prices were checked in November 2026.

Not sure you need this at all? Start with the complete guide to broadband backup. For help choosing a SIM and router, see 4G and 5G backup broadband.

What you need before you start

A mobile signal you have tested at the spot where the equipment will sit, on the network you plan to use.
A SIM that is activated and proven. Put it in a phone first, turn off Wi-Fi and load a web page. This rules out the most common fault before a router is involved.
A clear picture of your current setup. On full fibre (FTTP), a small wall box called an ONT connects by Ethernet cable to your router. On part-fibre (FTTC), the router plugs into the phone socket. On Virgin Media, the hub connects to a cable wall socket.
A note of anything plugged into your provider's router, especially a digital landline handset or a TV box. These stay where they are.
The admin details for your routers, usually printed on a label underneath.
One spare Ethernet cable.
An hour when nobody else needs the internet.
Optional: a battery unit, if power cuts are part of what you are protecting against.

Choose your route: three setups compared

	Route A: provider's backup device	Route B: 4G/5G router with a failover port	Route C: dual-WAN router
What you add	The provider's 4G unit or dongle	One router with a SIM slot and an Ethernet WAN port	A router with two WAN ports, plus a second connection
Works with	That provider only	Any provider	Any provider
Indicative cost	EE: £10 a month ⁹. Vodafone: included with Pro plans ⁴	Router from about £89 ⁷, plus a SIM	Router from about £49 (TP-Link ER605) to about £240 (DrayTek Vigor 2927) ⁸, plus the second connection
Setup time	10 to 15 minutes	About an hour	Half a day
Skill needed	None	Comfortable logging in to a router	Comfortable with network settings
Main drawback	Tied to the provider's router and contract	Adds a second layer of routing (double NAT)	More boxes and more to configure

Choose A if your provider offers it, you use the provider's router and you want no configuration. The provider options are compared in ISP backup vs DIY vs satellite.

Choose B if your provider has no add-on, or you want a backup that survives a change of provider. This is the right route for most homes.

Choose C if your second connection is another fixed line or a separate 5G home broadband hub, or you want finer control over how failover behaves.

Route A: plug in your provider's backup device

Check the provider's mobile coverage at your address. The backup uses the provider's own mobile network. EE's terms for Connectivity Backup refer customers to its coverage checker ³.
Order the add-on or the plan that includes it. EE sells Connectivity Backup as an add-on ⁹; Vodafone bundles its 4G Broadband Back-up with Pro plans ⁴.
Position and connect the device. EE's unit must be set up and kept plugged in, and the Smart Hub connects to it ³. Reviews of the EE and BT versions describe the unit linking to the hub by Ethernet cable or wirelessly ⁵¹⁰. A spot near a window often gives a stronger signal ¹¹. Vodafone's version is a dongle that plugs into the Pro router ⁴.
Confirm it is recognised. Check the lights on the unit and the provider's app.
Test it. Leave everything powered. Disconnect the cable that brings broadband into the router: the Ethernet lead from the ONT on full fibre, or the lead from the phone socket on part-fibre. Wait. For BT's Hybrid Connect, the switch has been reported at two to three minutes ⁵. If nothing has happened after five minutes, reconnect the cable and ask the provider's support how to verify the backup. Provider backups rely on the provider's own fault detection: EE says it monitors the connection and that the hub detects a problem and connects through the backup device ³, and Vodafone describes its backup as being for a total loss of fixed-line service ⁴.
Reconnect the cable and check that normal service returns.

Two things to know. The backup works only while you use the provider's router and stay with that provider ³⁴. And if you have a digital landline, ask whether calls continue over the backup.

Route B: a 4G/5G router with a failover port

The layout looks like this:

Internet line ─▶ provider's router ─▶ (Ethernet cable) ─▶ 4G/5G router ─▶ your devices
                                                             |
                                                         mobile network (standby)

Your provider's router stays exactly as it is. The new router sits behind it, takes its internet from it in normal times, and switches to the SIM when that supply stops. Your devices connect to the new router's Wi-Fi.

Why not replace the provider's router altogether? You can, but you would need your provider's connection settings, you may lose a digital landline that plugs into the provider's router, and support calls become harder. Sitting behind it avoids all three.

Insert the tested SIM into the new router while it is switched off. Place the router where you tested the signal and power it on.
Connect a laptop or phone to the new router's Wi-Fi, using the details on its label, and open its admin page. TP-Link's 4G and 5G routers use http://tplinkmodem.net or 192.168.1.1 ¹. Set a new admin password.
Prove the mobile connection first. With nothing plugged into the WAN port, load a web page. If it fails, the router may not have detected the SIM's settings; on TP-Link models you can create a connection profile under Advanced > Network > Mobile WAN ¹.
Change the operating mode so the router treats the Ethernet port as its main connection. On TP-Link models: Advanced > Operation Mode > Wireless Router Mode, then save and let it reboot ¹.
Change the new router's own address range if it clashes. If both routers hand out addresses in the same range (for example, both use 192.168.1.x), nothing will work properly. Set the new router's LAN address to something different, such as 192.168.10.1.
Cable the two routers together. Run the Ethernet cable from any LAN port on the provider's router to the WAN port on the new router. Set the new router's internet connection type to automatic (often labelled Dynamic IP).
Turn on the backup. On TP-Link models this is a switch labelled 3G/4G Backup (or 3G/4G/5G Backup). With it on, the router uses the mobile network when the main service fails ⁶.
Set up the Wi-Fi. Either choose a new network name, or reuse your existing name and password so devices join without being asked. If you reuse them, turn off Wi-Fi on the provider's router so devices cannot cling to the wrong box.
Move wired devices to the LAN ports on the new router.
Leave the landline handset and any provider TV box connected to the provider's router.
Run the tests in the testing section below.

About double NAT. You now have two routers in a row, each translating addresses between your devices and the outside world. This is called double NAT. Browsing, video calls, streaming and most work VPNs are unaffected. Online gaming, port forwarding and some peer-to-peer applications may complain. If that matters, look in the provider's router for a setting called DMZ and point it at the new router's address, or accept the limitation.

A known weakness. TP-Link's community pages document cases where its 4G backup did not switch over when the internet failed while the Ethernet link stayed up, or did not switch back afterwards, and ask users how they tested ². This is why the test routine below has two parts.

Route C: a dual-WAN router with two connections

The layout:

Line 1 ─▶ provider's router ─────────▶ WAN1 \
                                              dual-WAN router ─▶ Wi-Fi access points ─▶ your devices
Line 2 ─▶ 4G/5G hub or second router ─▶ WAN2 /

A dual-WAN router has two internet inputs and decides which to use. The TP-Link ER605, at about £49, and the DrayTek Vigor 2927, at about £237 to £242, are common small-office choices ⁸. DrayTek's "L" models have a 4G modem and two SIM slots built in, so the SIM goes in the router itself and nothing needs to plug into the second WAN port ¹².

Decide what will provide Wi-Fi. Wired-only routers such as the ER605 have no Wi-Fi of their own. Use access points, or an existing mesh system switched to "access point" mode.
Give every box a different address range. For example: provider's router on 192.168.1.x, the 4G or 5G hub on 192.168.8.x, and your own network on 192.168.20.x.
Connect both inputs. Provider's router to WAN1, second connection to WAN2. Set both to obtain their settings automatically.
Choose failover, not load balancing, if the second connection is a mobile one with a data allowance. Make WAN1 the primary and WAN2 the backup. The difference between the two modes is explained in the business guide.
Switch on connection detection for both inputs, as described in the next section.
Recreate your Wi-Fi on the access points with the name and password your devices already know.
Save a backup copy of the router's configuration to your computer.
Run the tests.

Set the failover rules: detection, thresholds, switching back

A router can judge a connection in two ways.

Link detection asks only whether the cable is live. It is instant but easily fooled: when your provider's network fails, the cable between your two routers is still connected and still "up".

Reachability detection sends small test messages (pings, or name lookups) to addresses out on the internet and counts the replies. This is the kind you want. If your router offers it, it may be called online detection, ping detection, link monitoring or health check.

Where the router lets you adjust it:

Targets. Use two well-known public addresses run by different organisations, so one company's problem does not trigger a false alarm. Public DNS services are the usual choice.
How often and how many. As a starting point, test every five to ten seconds and declare the line down after three to five missed replies. Faster settings react sooner but can flip to the backup during a brief wobble.
Switching back. If there is a delay or "stable for" setting, ask the router to wait a minute or two after the main line recovers before returning. Lines that are being repaired often bounce.
Alerts. If the router can send an email or app notification on failover, turn it on. Otherwise you may not notice you are running on a capped SIM.

Simple consumer routers may offer only an on/off switch for backup. That is acceptable, provided the test below shows it works in both failure cases.

Test it: the pull-the-plug drill

Run this when you first set up, after any firmware update, and every month or two.

Start something continuous on a laptop connected to your failover network: a video call with yourself on a second device, or a live radio stream.
Note your public IP address. Search for "what is my IP" and write down the answer.
Test 1: the cable comes out. Unplug the Ethernet cable between the provider's router and your failover router. Time how long it takes for the stream to resume.
Confirm you are on mobile. Check your public IP address again. It should have changed.
Plug the cable back in and time the return to the main line.
Test 2: the line dies but the link stays up. Leave both routers connected to each other. Now unplug the cable that feeds the provider's router: the lead from the ONT on full fibre, or the lead from the phone socket on part-fibre. The provider's router stays on, the link to your failover router stays live, but there is no internet behind it. This imitates a real outage. Time the switch.
Restore the line and confirm the router returns to it.
Check what you care about while on the backup: your work VPN, a video call, the printer, smart-home devices. Anything still connected to the provider's router's Wi-Fi will not have failed over.
Write down the timings. If Test 2 fails or takes minutes, revisit the detection settings, update the firmware, or reconsider the router.

A short freeze on a video call at the moment of switching is normal. The connection is moving to a different network with a different address.

Keep it alive in a power cut: battery for the fibre box and router

Trace the chain your data follows: ONT, provider's router, failover router or backup device, any Wi-Fi access points, then your laptop. Every mains-powered link in that chain must stay on, or the backup is useless when the lights go out.

Your options:

A battery unit from your provider. If you depend on your landline, your provider must give you a way to call the emergency services in a power cut that lasts at least an hour, and some provide units that last up to seven hours ¹³. Ask what you are eligible for.
A small 12-volt DC battery unit (often sold as a mini UPS) that sits between a device's power adapter and the device. These suit a single ONT or router. Check that the voltage and plug match your equipment exactly.
A conventional UPS with mains sockets, which can run several boxes from one unit.

To estimate running time, divide the battery's capacity in watt-hours by the combined power draw of the devices in watts, and allow a margin for losses. For scale, one battery unit adopted by several UK providers in 2025 was specified to run a 25-watt router for seven hours or a 55-watt router for four ¹⁴. The wattage of your own equipment is printed on its power adapters (volts multiplied by amps gives the maximum).

Be realistic about what this achieves. With a battery, your home equipment rides through a power cut. Whether the mobile network does depends on the mast: Ofcom's guidance, revised in June 2026, sets expectations for operators' backup power but no fixed number of hours ¹⁵¹⁶. A local cut is usually survivable; a regional one may not be.

Test the battery the same way you test the failover: unplug it from the wall with everything running and see how long it lasts.

Stop the backup eating your data allowance

Know your limit first. Vodafone's backup includes 100 GB a month ⁴. EE's backup device contains an unlimited-data SIM ³. With your own SIM, the limit is whatever you bought.

If the allowance is capped, do these when you fail over:

Pause cloud backups and photo syncing on computers and phones.
Postpone operating-system and game updates. Game updates in particular can be very large.
Ask the household to hold off on streaming, or lower the picture quality in each app's settings.
Turn off HD video in meetings if you are counting gigabytes. A one-to-one 720p call uses roughly 1.1 GB an hour on Zoom's published figures; standard quality uses about half that ¹⁷.
Use the router's controls if it has them: block the guest network, or allow only named devices while on the backup.
Set a data alert in the router or the mobile provider's app.

Afterwards, check that the router has returned to the main line. A router stuck on the backup ² will quietly use the SIM for everything.

Troubleshooting

Symptom	Likely cause	What to do
Works when you pull the cable, but not in a real outage	The router only detects a dead link, not a dead internet connection	Turn on or adjust reachability detection; update firmware; see the known issue reported for some TP-Link models ²
Stays on mobile after the line recovers	Failback has not triggered	Restart the router; update firmware; check the switch-back setting ²
Some devices go offline during failover	They are still joined to the provider's router's Wi-Fi	Move them to the failover router's network; turn off Wi-Fi on the provider's router
No internet at all after setting up	Both routers use the same address range	Change the LAN address range on the new router
Mobile works alone but never as backup	Wrong operating mode, or the backup switch is off	Set Wireless Router Mode and turn on the backup option ¹⁶
SIM will not connect	SIM not activated, PIN lock, or settings not detected	Test the SIM in a phone; remove the PIN; create a connection profile ¹
Work VPN drops and will not reconnect	Your public address changed, or the mobile network's shared addressing blocks it	Reconnect manually; ask your IT team whether the VPN works over mobile networks ¹⁸
Cannot reach home cameras from outside while on backup	Mobile networks share addresses (CGNAT), blocking inbound connections ¹⁸	Use the camera's cloud service; see the limits section of the mobile backup guide
Backup is slow	Weak signal or a busy mast	Move the router to a window or upstairs; test another network
Games console reports strict NAT	Double NAT	Put the failover router in the provider router's DMZ

Keeping it working. Once a month, repeat Test 1. Check that the SIM is still active and has data left; pay-as-you-go data packs expire after a fixed period ¹⁹. Install firmware updates when offered, then re-test. Run the battery test twice a year.

FAQ

Do I have to replace my provider's router?

No. In Routes B and C the provider's router stays in place and the new equipment sits behind it. That keeps your landline and your provider's support arrangements unchanged.

How long does failover take?

It depends on the equipment and settings. BT's provider backup has been reported at two to three minutes ⁵. With your own router, the time is governed by how often it tests the line and how many missed replies it waits for. Measure yours with the drill above.

Will my video call survive the switch?

It will usually freeze for a few seconds and then rejoin, because the connection moves to a different network. If the switch takes minutes, the call will drop and you will need to rejoin.

Does double NAT matter?

Not for browsing, streaming, video calls or most VPNs. It can affect online gaming and anything that needs ports opened from outside. Using the DMZ setting on the provider's router usually resolves it.

Will my smart-home devices fail over?

Only if they are connected to the network that fails over. Devices left on the provider's router's Wi-Fi go offline with the line. Move them to the failover router's Wi-Fi.

How do I know when I'm on the backup?

Check the status page of the failover router, turn on its alerts if it has them, or look up your public IP address: it changes when you are on the mobile network.

Can I use this setup for a small business?

The principles are the same, but a business also has to think about phones, card payments, fixed IP addresses and service agreements. Those are covered in Business broadband backup.

Sources

Checked 13 November 2026.

TP-Link, "How to set up TP-Link 5G/4G Router on web management page" (updated 26 May 2026): tp-link.com
TP-Link Community, "3G/4G Backup failover issue for LTE Gateway/Deco 4G/5G products": community.tp-link.com
EE, "Connectivity Backup" terms and conditions, December 2025: ee.co.uk
Vodafone, "Pro Broadband" (4G Broadband Back-up terms): vodafone.co.uk
Broadband.co.uk, "What is hybrid broadband?": broadband.co.uk
TP-Link, "How to set up 3G/4G/5G Backup on TP-Link LTE router under wireless router mode": omadanetworks.com
PriceSpy UK, TP-Link 4G/5G router listings (viewed November 2026): pricespy.co.uk
Mighty Gadget, "Best dual WAN routers" (TP-Link ER605 and DrayTek Vigor 2927 listings): mightygadget.co.uk
EE, "EE Home Price Guide" (add-on prices, April 2026): ee.co.uk
Yahoo Lifestyle, "EE Smart Hub Plus wireless router review": yahoo.com
Ken's Tech Tips, "BT Hybrid Connect": kenstechtips.com
ProVu, "DrayTek Vigor 2927 Router Series": provu.co.uk
Ofcom, "Future of landline calls": ofcom.org.uk
ISPreview, "Broadband ISPs Vodafone, BT, KCOM and Zen Internet Prep New UK Battery Backup", 14 March 2025: ispreview.co.uk
Ofcom, "Statement: Network and Service Resilience Guidance" (last updated 16 June 2026): ofcom.org.uk
Osborne Clarke, "Telecoms: UK Regulatory Outlook July 2026", 29 July 2026: osborneclarke.com
Zoom, system and bandwidth requirements: developers.zoom.us (bandwidth table as reproduced at colum.teamdynamix.com)
EE Community, thread on public IP addresses and CGNAT on EE mobile broadband: community.ee.co.uk
Three, "Contract summary: Pay As You Go Mobile Broadband SIMs": three.co.uk

General information for UK households and small businesses, not legal, financial or technical advice. Facts checked on 13 November 2026; prices, coverage and rules change, so confirm the details with a provider before you buy.

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