r/HomeNetworking • u/Greg_HoppityWoo • 13h ago
Unsolved Sudden Powerline speed drop (from 80 to 40 Mbps) overnight, while Wi-Fi works perfectly. Any idea what the cause could be?
Hey everyone, I’ve been losing my mind since yesterday trying to troubleshoot a weird home network issue, and I'm hoping someone with more experience regarding electrical wiring or Powerline adapters can give me some insight.
I have a VDSL/FTTC connection (TIM, an Italian ISP) that usually runs at a rock-solid 75/80 Mbps download. My house has two floors. My desktop PC is upstairs, and it has always been connected via Powerline adapters (Ethernet from the router to the first adapter downstairs, and Ethernet from the second adapter to my PC in my room upstairs). For months, it worked flawlessly at full speed (75-80 Mbps).
Starting yesterday, out of nowhere, the speed on my PC cut exactly in half and won't go past 40 Mbps.
I’ve already done a ton of troubleshooting to isolate the issue:
- Wi-Fi Test: If I run a speed test on my phone or even on the PC itself using Wi-Fi (I have a Gigabyte B650E Aorus Elite X AX with built-in Wi-Fi), the speed flies at 86 Mbps with a 6 ms ping. So the ISP connection and the router are working perfectly.
- Ethernet Cables: Tried replacing the cables with CAT 6 ones, but it made no difference.
- PC Network Card Check: Windows correctly negotiates the connection at 1.0 Gbps Full Duplex. I also tried uninstalling the network adapter drivers, doing a complete Windows network reset, and flushing the DNS cache. Nothing worked.
- Powerline Hardware Test: I took the upstairs Powerline adapter downstairs and plugged it into my PS5 in the same room as the router. I re-paired them there, ran a test, and the PS5 hit a full 79 Mbps. This proves the Powerline hardware itself is totally fine and not broken.
- Switching Outlets Upstairs: I tried moving the Powerline adapter to a different outlet in my room using a heavy-duty extension cord, but as long as it's upstairs, it caps out at 40 Mbps.
- New Appliances/Devices: Absolutely nothing new has been plugged in anywhere in the house (no phone chargers, appliances, smart LED strips, etc.) over the last two days.
To sum it up: the ISP line is fine, the Powerline adapters work when they are close to each other, and my PC is configured correctly. But the second the adapter goes back to my bedroom, the speed gets throttled to exactly 40 Mbps.
Since I’ve temporarily fixed the issue by switching to my motherboard's Wi-Fi (which is working amazingly well), I'm just purely curious at this point: what on earth could have happened overnight to the electrical wiring or the circuit leading to my bedroom to cause such a specific, consistent 40 Mbps hard cap? Has anyone experienced anything similar?
Thanks in advance for any insights!