WiFi signal suddenly weakened

[#1]

Until yesterday lunchtime, the WiFi signal from the router reached across the house.  Then suddenly it only got halfway and devices further away were unable to connect.  It seems to be getting worse and we appear to have to be almost withing eye-sight of the router for it to work.  Nothing else has changed.  Can router's WiFi circuits fail like this?

[#2]

Maybe you have a neighbour with a new WiFi device using the same channel as you ?

Try changing the WiFi channels in your router to see one which gives you the best range.

Changing your Hub Two wireless settings - Plusnet Help 

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[#3]

I can see no other network that is in range, so I don't think a neighbour is the problem.  My Technicolor router does not appear to have any means of changing the WiFi frequency (it says 2.4 GHz with no option to change it).

[#4]

🙄    Changing the wireless channel on your Technicolor TG582n router - Plusnet Help 

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[#5]

Ah, OK.  I've tried that and it makes no difference.  When the device is moved away, the plusnet connection says "out of range" and there is nothing else of significant strength showing.