@BillComer 

Hey Bill

While i have not personally tried this, to the best of my knowledge the Powerline contained in the Deco P9 cannot be synced with other Powerline adaptors.   The P9s can only connect to other P9s

Thinking out loud here, if you have 5 powerline adaptors at present and simply want to add "mesh" wifi with roaming etc.. then really ANY of the deco might be a cheap solution for you

On your current adaptors just disable the WiFi and plug in a Deco via the LAN connection, use this to send the WiFi.

Set the new Decos in Access Point Mode so they use the LAN cable to connect (via your existing home plugs) and all should be good.

If you had 3 to 5 of the Deco S4 it should offer similar coverage / performance as the P9s would.   The S4 is a very capable device, just lacks powerline built in which you do not need (as you will be using your existing powerline adaptors)

  @Philbert 

Thanks for the reply.

My bad description. That is pretty well what I was thinking.

IE: turn the wifi off on the old units & just use them for the powerline network.

So I think I will give that a go with  P9s or as you suggest P4s 

  @BillComer 

Hey

Personally, if i was in your scanario i wouldnt choose the P9s.   The P9s come with PowerLine adaptors built in which is their main selling point, depending on how you set this up they could interfere with your existing plugs.    Ideally you are looking to use your exisitng plugs therefore negating the advantage of the P9s.  You are paying for something thats not needed imho

The M5 would be my choice as they are very capable and as quick as the P9s, but without powerline so therefore cheaper!

However as mentioned i have used the S4s in many a setup, they are really cheap and offer good wireless coverage vs price..  get 5 of these for the same price as 3 M5s and litter the place in WiFi  

  @Philbert 

All installed exactly as you suggested. 

Disabled the WiFi on the old power lines. 

Plugged the s4s into the old powerlines. 

Job done. 

They appear to be more powerful than my old wap8630p as I now have reasonable reception in the garden. Result, saves me drilling through 3ft thick walls. 

Thanks again. 

  @Philbert Spoke to soon.

I do appear to have an issue with wifi calling now . My phone was saying ;'emergency calls only'

I have just been playing on the router with port forwarding & port triggers, based on https://www.tp-link.com/uk/support/faq/1259/

(never done this before) & my phone now says 'no service'.

Not sure if this is caused by the mesh systems or not.

I will carry on playing

  @BillComer 

Try going to setting on the Deco app, then advanced and disabling SIP ALG

Gut feeling I had to do that once for a customer..

Otherwise glad the mesh system appears to be working for you, yeah the S4 are good wee units for the price!  

  @Philbert 

I wake up, the sun is shining and it's glorious. 

What's more, this morning I have WiFi calling. I'd swear that when I left it it did not work and I'd swear I changed nothing since. 

But I have made changes and it works. I might play more to see if it was me or the phase of the moon. 

Anyway I now have the deco set up as a router despite them just connected to the house network via powerline straight into my old router. 

I have also set up port forwarding for 4500:udp, 500:udp and 143:tcp

But as I say I am sure I tested this config last night. 

Thanks again. 

  @BillComer 

Happy days!   No worries happy you got sorted and glad to help