It’s not the smart meter that’s the problem. It’s the powerline extenders being fussy. I’ve seen this problem before and it’s made worse because powerline wi-fi extenders are often:

1. Notorious messing up either themselves or literally everything else for completely random reasons
2. Running on a dead standard (HomePlug Alliance died a few years ago)
3. Made from cheap parts that don’t perform well

Unfortunately, the only solution is to get rid of them and get something else like Ubiquiti UniFi (or AmpliFi), Netgear Orbi, TP-Link Deco or something else along those lines.

If your powerline extenders only do 2.4GHz, it’s probably worth replacing them anyway. I suspect the 2.4GHz band in your environment is just so crowded by too much stuff that you’d be better off using the 5GHz band for Wi-Fi purposes. The Ubiquiti WiFiman app can help you scan the environment to see how badly jammed up it is.

I suppose replacing them is the easiest solution but they weren't fussy before the smart meter installation in fact they worked really well with very good speeds and never dropping in and out. 

But they share the 2.4GHz Band... Which has tons of other stuff as well 

I can't imagine they share that much as I only have fire sticks and a fire TV that uses the broadband and even then there's only ever one on at a time and one mobile phone which when I go into it's wifi settings is using 5ghz.

I'm not doubting what you are saying about the technology these extenders use being old. I just wish the information that the Smart meter might cause problems/interfere had been mentioned.

I was getting speeds around 100mb now the highest is 17 and lowest is 3, this is in my detached garage which is why I find it particularly annoying.

Anyway I will look into those systems you mentioned as  way of restoring a usable signal. 

You’re suggesting that connecting via the 2.4GHz band is to be avoided because of this other stuff. My Android phone seems able to pick up what it thinks is the best signal and connects to the router at 5GHz. My Windows laptop does the same and almost always chooses 2.4GHz. So what ‘other stuff’ should I be trying to avoid (and how?)? Bluetooth? Zigbee? Microwave oven? 

The only way a 2.4GHz Band can get 100mb/s is if your extenders were using 40MHz Channel Width via Channel Bonding, which I like to call Bad Neighbour Mode. It’s known to cause a ton of problems and is best avoided. 20MHz Channel Width (aka Good Neighbour Mode) leaves more space for other stuff. The more things you add, the worse that problem gets. I suspect there’s a clash being caused because of that.

It’s also worth bearing in mind that Bad Neighbour Mode affects your neighbours as well. Unless you live in the middle of nowhere, it’s better to use a 20MHz Channel Width on the 2.4GHz band. You can usually use 80MHz or possibly 160MHz Channel Width for the 5GHz band though.

I don’t consider this an issue with smart meters, but more other (mostly legacy) stuff not playing by the rules. Given that there’s nothing that DCC or energy suppliers can do because they can’t access your kit, it’s unfortunately down to you to resolve. I can’t really see how telling people that smart meters mess up wi-fi will fix anything when it’s already explicitly designed to avoid causing issues.

That sounds more like your laptop being fussy about not using 5GHz but some driver updates might help with that. While it can be possible to try and suggest that high-performing clients (like your laptop) to use 5GHz, it’s very difficult to force them to use it unless you have Band Steering capability on the access points. Not everything has this - especially the cheap ISP routers. But yes, there is an absolute ton of stuff on 2.4GHz including all those that you mentioned. You can’t totally avoid it, so you just have to try and keep to Channels 1, 6 and 11 and hope that no-one uses any others outside of those three.

5GHz is a bit cleaner, but most people can’t use the entire spectrum due to DFS Channels. Only fancier access points can use those but they have to comply with strict rules.

I run a ton of Ubiquiti UniFi kit in my flat, so I can scan the environment. Here’s an example of the difference.

2.4GHz can still be used (especially for longer range), but if you want faster speeds and less interference, 5GHz is the way to go.

Ok I also don't see where telling people that smart meters don't interfere with the WiFi signal of PL extenders when clearly they do, whether it's old tech or not, they worked perfectly well before SM installation and now the performance has been severely impaired. If you took a car in to be serviced and they fitted a new ECU claiming it to be far superior to the original ECU and then you found your mpg figures were 17mpg instead of the usual 100mpg  I'm pretty sure you'd be blaming the new ECU and not the fuel pump or whatever.

I will try switching to the 20mgz channel and see if that makes it more stable. 

That’s because it’s not the smart meters interfering - your powerline extenders are the root cause of the interference. If you look at the results from the RF Scan that Mega Exploud did, there’s a huge clue.

The 20MHz Channel Width on 2.4GHz allows for 13 Channels, with five possible combinations that don’t clash:

• 1, 6 and 11
• 2, 7 and 12
• 3, 8 and 13
• 4 and 9
• 5 and 10

But the 40MHz Channel Width allows for only one combination that won’t clash. Nothing else can fit in that same space without clashing. And since ZigBee tries to use something like 10MHz Channel Width and Channel Agility, it can easily squeeze into gaps between 20MHz Channel Width, but not 40MHz Channel Width.

By running at least two APs at 40MHz Channel Width on the 2.4GHz Band, you’re gobbling up the entire spectrum and that’s just asking for trouble. The ZigBee HAN is trying to find a safe gap but can’t because your extenders are using up everything, so it’s forced to slice through your channels and in turn, results in clashes. That’s why I call it Bad Neighbour Mode because it basically kills all the neighbours Wi-Fi experience and knocks out everything in the area.

Mega Exploud runs scans that shows all the possible combinations and as you can see, under my environment they’re all in use with tons of 20MHz Channel Width devices.

Ok so I set it to  20MHz and it has made no difference. Maybe a little more background would help... I live alone and only watch one tv at a time, I don't have Smart plugs etc. My phone favours 5 not 2.4. It is secure so no neighbours piggy backing so I'm struggling to see why my 2.4 would be too busy to provide a decent signal when it was perfectly fine before. I get what you say that they are designed not to cause problems and that the TP-Link extenders are old tech but they were there before the smart meter and coped perfectly well with the very minimal traffic that went through 2. 4.

Now to top it all the online chat and landlines are closed. 

Unimpressed as there are several issues with the meter apart from the one discussed here. 

Just miffed I need to spend time and money to fix a problem that wasn't there before the installation of the SM but unavoidable now so ho hum.

Ok so I set it to  20MHz and it has made no difference. Maybe a little more background would help... I live alone and only watch one tv at a time, I don't have Smart plugs etc. My phone favours 5 not 2.4. It is secure so no neighbours piggy backing so I'm struggling to see why my 2.4 would be too busy to provide a decent signal when it was perfectly fine before. I get what you say that they are designed not to cause problems and that the TP-Link extenders are old tech but they were there before the smart meter and coped perfectly well with the very minimal traffic that went through 2. 4.

Now to top it all the online chat and landlines are closed. 

That’s because it’s a Bank Holiday today.

It’ll take up to 24 hours for the ZigBee HAN to re-scan the environment and adjust itself, so please allow it some time to catch up. It’s designed so that it doesn’t keep flipping all over the place for no reason. Even my own Ubiquiti UniFi kit only does automatic re-optimisation once a day for the same reason.

20MHz Channel Width also has a theoretical maximum speed of around 54mb/s on the 2.4GHz Band. In reality, you can expect speeds more in the range of 20mb/s.

Ah that would explain, we don't get it here, well my company hasn't given it anyway so I forgot about it. 

Does the meter need to be connected to my home WiFi, I thought they had their own independent signal? 

Nope. In actual fact you can’t connect it to Wi-Fi either. But the IHD might be able to do that depending on which one you have. The ZigBee HAN is how the meters communicate with each other, the Comms Hub and the IHD and there’s a dedicated WAN that connects them to DCC separately from everything else.

One other thing. If you do go for UniFi, don’t get tempted by the cheaper UniFi Dream Router. It’s a watered down version of the UniFi Dream Machine and isn’t worth the cheaper price - the UDM is massively superior to the UDR and is worth the extra £100.

Would manually selecting a channel for 2.4 to use work if it was not a channel that the SM used? My meter is a Landis EDM1 so is there any way of knowing which channel or channels it is using?

Probably not much effect, but you can do it if you wish. I recommend Channels 1, 6 and 11 if you’re going to set it manually. You’ll need to set each AP to a different channel to avoid clashes and make sure they all share the same Channel Width.

That’ll give plenty of free space for ZigBee to work with and the HAN should then slot itself into the space made available.