@Bafflled 

Thanks for reaching out. I understand that you are experiencing weak Wi-Fi signal in your garden room, likely due to the aluminum construction, and have tried adding additional Deco Mesh units and a Powerline adapter, but the signal remains poor and other units lose connectivity when you attempt to connect via Ethernet.

To improve Wi-Fi coverage, especially in challenging areas like a garden room with metal construction, please consider the following tips:

1. Placement of Deco Units:
• Avoid placing Deco units in enclosed spaces such as cabinets, shelves, or corners. Position them in open areas for optimal coverage.
• Keep Deco units away from large metal objects, as these can block or interfere with wireless signals.
• Do not place Deco units near Bluetooth devices, cordless phones, or soundbars, as these can cause interference on both 2.4GHz and 5GHz bands.
• Place Deco units at desk or table height, rather than on the floor or near the ceiling, for best signal propagation.

2. Checking Signal Strength:
• Use the Deco app to check the backhaul signal strength of your satellite units. A 2-bar signal is generally acceptable. If you see only 1 bar, move the satellite closer to the main Deco or another satellite unit.

3. Avoid Overlapping Coverage:
• Do not place two Deco units too close together (such as in the same room or adjacent rooms). Typically, one Deco unit can cover 1-3 rooms.

4. Expanding Coverage:
• If coverage is still insufficient after optimizing placement, consider adding more satellite units to extend coverage, especially to difficult areas like your garden room.

5. Powerline Adapter Considerations:
• Powerline adapters can be affected by the quality of your home's electrical wiring, the use of extension cords or adapters, and the distance between outlets. For best results, plug Powerline units directly into wall sockets, avoiding extension leads or adaptors whenever possible.

If you have already tried these adjustments and still experience weak signal, you may want to share your house layout with TP-Link support for more tailored advice.

For more details, you can refer to the official FAQ: https://www.tp-link.com/support/faq/3480/

Let us know if you need further assistance!