Sudden reduction in wifi signal strength

[#1]

We've had Plusnet broadband for several years. Normally the signal is good throughout our home, even at the points furthest from the router. Over the past 3 days the signal strength has reduced so that wifi is only available to use in the room where the router is. Nothing else has changed about our set up during this time. 

I spoke to Plusnet and they suggested I change the wireless channel, I've tried this but things are no better.

In the rooms where we can't use wifi, sometimes there appears to be a couple of bars of wifi signal but no connection. Sometimes the connection appears in Settings and I'm asked for the password but again, no connection occurs.

Any suggestions? Thanks!

[#2]

@Jd

Most likely a new source of interference.

If you have an Android device, there are various "WiFi Analyser" type applications which can show you what is going on.

Sometimes Bluetooth interacts with WiFi so I wonder if you have a new Bluetooth device.

[#3]

A wifi analyser app will not show which other networks are new and which have been there a long time. One useful thing they do show is the actual signal strength, if it's lower than about -60 dBm, then that's not enough for a reliable wifi connection.

What router is it, and how old is it? It's possible it has become faulty, especially if strength of the signal it transmits has reduced.

[#4]

Hi, it's the TG582n. We have some Bluetooth devices but as far as I can see they're all off. I've walked around the house and there's a definite limit to the signal of about 10 metre- previously we could use the wifi outside in the garden! 

Do do I need a new router?

[#5]

Use a free app such as InSSIDer to show what channels in use in your immediate vicinity; maybe
someone has suddenly used your channel or adjoining one. The app will show which channels are
free; switch to one of those. Unsure if yours is a dual band router, but generally the 5ghz band is less
populated, but has lesser range than the older 2.4ghz one.

[#6]

@ejs as you say, the WiFi analyser won't identify new sources of interference but it provides some clues about channel choice.

@Jd If you have "standard" broadband, you could get a replacement router to try quite cheaply on eBay (or borrow one/use an old one).

I would look for one that also does the newer 5GHz WiFi band. A BT Home Hub 5 seems to go for less than £10 on eBay and would probably be worth a try.

There are instructions on using a Home Hub 5 on Plusnet.

https://community.plus.net/t5/My-Router/Use-a-BT-Hub-2-3-4-or-5-on-a-Plusnet-connection/td-p/1192234

[#7]

Update:

Thank you you everyone for taking the trouble to reply. I decided to turn off the router for a few hours yesterday, and since being turned on again the wifi is back to normal. Not sure why this should be, maybe the router was overheated, or something?