Router only covers a tiny bit of the house?

[#1]

Thanks for your help @Bogbody as you might have guessed, I've got no idea what I'm doing when it comes to wi-fi, broadband etc!  

Since I moved in and installed the Plusnet router I had intermittent problems with the 2.4GHz.  Some days fine and some days every 5 minutes everything would be extremely slow or I couldn't access the internet at all.  This would happen even if I was in the same room as the router.  After a while it would be back to normal.

When I told Plusnet they just suggested I use 5GHz instead which has been stable with no dropping out.  But it looks like it's going to be more difficult to extend the signal for that band.... 😞

I've checked channels and it looks like next door one way is using 1 and other way is using 6 so I've changed to 11 but that hasn't helped the signal strength.

[#2]

Difficult one @katesam 

See how many Wi-Fi networks are around where you live, it is possible one is interfering with yours.

[#3]

Thanks @Alex 

Only 1 other network shows up in wifi settings for phone, laptop etc.  I scanned on WifiInfoView and that shows 3 more networks (all Virgin Media). How can I tell if one of them is interfering with mine?  This afternoon I switched my 2.4GHz band from channel 1 (which next door is using) to channel 11 (which only 1 other network is using) and tried that out again instead of the 5GHz band.  But I've already had a couple of issues of very slow connection and one brief loss of connection - same as before.

[#4]

A sudden drop in data rate when another router/hotspot/random wifi device signal appears. Sometimes only by noticing a pattern - only after school time or only in the evening for example.
You have to remember that the other person may not be aware of a problem. However, there are idiots that deliberatly use kit to jam wifi. !!!!
Some of the wifi apps will suggest a channel to use. If you have intermittent interference try to check the coverage when its not working properly. You may have a neighbour using a bit of kit (like a hotspot router or wifi printer) that causes interference only when its in use???
Sounds to me like you would be better investing in 5GHz kit????

[#5]

None of my Wi-fi stuff supports 5GHz "kit", including my mobile and a couple of laptops. Changing my "kit" would be slightly pricey - and not guaranteed to work, anyway.

My router has its 5GHz feature disabled by me.😀

[#6]

@Bogbody thanks for the TP Link suggestion.  Just got a dual band ac wifi kit and with the extender upstairs I now get decent wifi up there (not just in the room above my router!).  The back of the house downstairs still needs a boost so I'll get another one for back there and hopefully will have normal wifi throughout the house