@Swoosh2023 

Start with the following TP-Link document: General Questions about the Powerline or PLC Backhaul Feature of Deco

With your setup, at least in theory, using Deco P9 should be easy. No extra hardware is necessary, but you must not have other types of powerline adapters sharing electric wiring with P9s.

Unplug TP-Link TL-WPA8630P powerline adapters in office and garage. If there are other powerline adapters - unplug them, too. Plug Main Deco P9 (Office) and Satellite Deco P9 (Garage) to the same electric outlets powerline adapters TL-WPA8630P were plugged to. Check status of Satellite Deco P9 (Garage) backhaul link in Deco app. See How do I know if the Powerline Backhaul is working?

I checked TL-WPA8630P specs: it is powerline adapter set with WiFi. If they were working as shown in your network diagram, that means you had WiFi signal in garage. What was the reason to replace them with Deco P9?

  @Alexandre. Thank you for takng the time to response - appreciated.

The reason we went for a P9 is we wanted a mesh network to make the moving around the house more seemless.  The individual power line adaptors with Wifi as highlighted in the diagram were not as feature rich as the Deco units and movement between different the different WIFI network not so seemless.

We have setting up the Deco P9 units with nothing else plugged in i.e.any other network over powerline devices.  No change - P9 does not use powerline.  Using the TP-Link adaptors on exactly the same power sockets gives us network over power cables.  This makes us believe the powerlines are just fine.

The TP-Link adaptors are configured with WIFI disabled and now simply providing ethernet backhaul to the Deco P9 devices.

The thinking out loud question I have right now is perhaps we should return the Deco P9 devices and get something which is less expensive and aesthecially a little easier on the eye like the Deco M5 devices if we will use other hardware to provide the backhaul over ethernet.

But you have at least confirmed that I'm not imaging that this simply should have worked out of the box which, unfortuntely, it currently is not.

Thanks again.

  @Swoosh2023 

Deco P9 should have worked out of the box. It is very hard to troubleshoot powerline issues, so if P9 can't establish powerline link it makes sense to just return them. 

Try (check) two things before packing and sending back Deco P9s:

1. In Deco app, check Update Deco page under More/System. See if there is firmware update for P9 - if it is, update P9s and maybe that'll enable powerline link.

Also, check that Update Deco screen reports your Deco mesh consisting of P9s and only P9s. I've been on this forum long enough to see people who thought they are buying one Deco model only to find they've got different Deco model.

2. After confirming with Deco app that it is P9s you have, bring Garage P9 to the office where Main Deco is and plug Garage P9 to the power socket in that same office room on same circuit breaker as Main Deco. If that won't bring powerline link between these two P9s, nothing else will. 

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I am running Deco mesh at my house that consists of M5 and M9 Plus Decos. M9 Plus is like big brother to M5: same form factor, a tiny bit larger, with faster WiFi speeds, but costs more. If your Internet speed above 500Mbps, in addition to M5 you can also consider M9 Plus.

I tested Deco M5 with powerline adapters, it handles them just fine. Just like P9, it'll report Ethernet backhaul when connected through TP-Link powerline adapter. Out of all WiFi5 Deco models M5 is the most feature rich. 

  @Alexandre. Thanks again for the reply.

1.) Have tried almost all permutations on the P9s and sockets and nothing seems to bring powerline into play.  The fact that the exact same sockets (plus others) gives positive results for other TP-LINK devices doing network over power seems to strongly imply the powerline circuits are good.

2.) 100% confirmed that all devices are indeed Deco P9s with the latest firmware (1.1.3) installed.

As for the M5 devices - yes am also a big fan and would be my preferred choice.  Bought the P9s explicilty because they claimed to support network over powerlines out of the box but alas it's not to be.  Thankfully we had the exisitng equipment to get us something up and working.

I'll check this thread in a few days to see if anyone from tp-link has any ideas and then decide what to do next.

Regards

  @David-TP 

Hi David,

The powerline connectivity doesn't work on any socket either inside the house or the garage. It just happens that is where I wanted to use the powerline connectivity.

As for beta firmware - doesn't really appeal for a product which I paid non beta money for :-(

Oh well.