troubleshooting

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Your wifi has not died. That is the maddening part. It connects, you start something that matters, and then it drops, comes back, drops again, like a sulky teenager who will answer you but only when it suits.
Dead wifi is a different problem, and if yours never connects at all, start with wifi that will not connect. This page is for wifi that works and then keeps cutting out.
The ten-reasons listicles never tell you this. The pattern of the drops tells you the cause. Drops everywhere, drops on one device, drops in one room: three different problems with three different fixes. Read your pattern, start with the most likely cause, stop when the drops stop.
Before anything else, sixty seconds. Plug a laptop into the router with an ethernet cable and use it while the wifi is dropping.
If the wired connection holds rock steady, your line is fine and the problem is genuinely your wifi. Carry on down this page. If the wired connection drops too, it is not wifi at all, it is the broadband line, and you want when the line itself keeps dropping. Same symptom for you, completely different fix.
While you are there, reboot the router. Unplug it, count to thirty, plug it back in. It clears the router's temporary memory and re-establishes the connection to your provider, and it fixes more intermittent wifi than any other single thing. It is the lowest-effort move on the page, so do it before you read on.

Most intermittent wifi is a signal problem, and the giveaway is geography. The drops worsen the further you get from the router, or they happen in one stubborn room and nowhere else.
Wifi is radio, and radio fades with distance and through walls. A thick internal wall, a chimney breast, a mirror or a foil-backed insulation board will flatten a signal that was perfectly healthy one room over. The router stuffed in the cupboard under the stairs next to the meter is fighting the whole house.
Move it first. Get it up high, out in the open, roughly central to where you actually use the internet. Then check you are on the right band. Most routers broadcast a 2.4GHz network and a 5GHz one. The 5GHz band is faster but does not travel as far; 2.4GHz is slower but reaches further through walls. For a far room, force the device onto 2.4GHz; for a drop next to the router, try 5GHz.
If a room is simply too far, no amount of fiddling beats physics. That is what a mesh system or a booster is for, and most providers sell their own. A wifi speed test from the bad spot and again next to the router tells you whether it's range or your actual speed.
If the drops cluster in time rather than in space, suspect interference. The classic tell is the kitchen. Someone puts the microwave on, the wifi staggers, the microwave stops, the wifi recovers.
That is not a coincidence. Microwaves, baby monitors and plenty of other household kit run on the same 2.4GHz frequency your wifi uses, and they shout over it. In a block of flats it is worse, because every neighbour's router is crammed into the same 2.4GHz band, which has only three channels that do not overlap each other.

The fix is to get off the crowded band. Switch the device to the 5GHz network, which has far more room and which the microwave and most of the neighbours are not sitting on. If your router only does 2.4GHz, dig into its settings and change the wifi channel to 1, 6 or 11, the three that do not interfere with each other. Most routers pick a channel automatically, and automatically is not always sensible.
Wifi that is fine all day and falls apart after dinner has two suspects, and they are not the same.
One is peak-time congestion. The whole country comes online roughly 7pm to 11pm, the network fills up, and everyone slows down. That is your provider's network, not your wifi, and no amount of router-shuffling touches it.
The other is that 2.4GHz interference spikes at night too, because every neighbour's phone, tablet and telly comes online at once and crowds the band. To tell them apart, run a wired speed test at 9pm and again at 11am. If the wired speed is healthy at night, your line is fine and the evening trouble is local wifi congestion, so move to 5GHz. If the wired speed sags at night as well, it is network contention, and that is a slow-broadband and possibly a switching question, not a wifi one.
Least common, but real. If the drops hit one device while everything else stays online, the fault is on that device, not the router. Tell it to forget the network and rejoin with the password, which clears a stale saved profile and forces a clean reconnect. If that does not hold, update the wifi driver on a laptop or the operating system on a phone, and check the router has its latest firmware.
If every device drops and a reboot only buys you a few days, the router itself may be tiring, and an ISP-supplied box years past its prime is a fair suspect, and whether you actually need a better router is worth a look before you replace it.
If the wired connection drops alongside the wifi, this was never a wifi problem. Check whether your provider is down in your area, then report it. Under Ofcom's automatic compensation scheme, if you lose service completely and your provider does not fix it within two full working days, you are owed £10.34 for each day it stays broken, and £32.31 if an engineer misses an appointment. It pays as a bill credit automatically once you have reported the fault. Many of the largest providers including BT, Sky, Virgin Media, TalkTalk, EE, Vodafone and Plusnet are signed up, though smaller altnets often are not, so check yours. The full rules are on Ofcom's compensation page.
And if the verdict is that the line, not the kit, is the thing letting you down night after night, that is the point where fixing stops and switching starts.