Powerline adapters - unstable performance!

I have a pair of Zyxel PLA4201 powerline adapters bridging our Virgin Super Hub in one room upstairs (where the Virgin broadband wall socket is located) to a second wifi router downstairs acting as a secondary access point. If I connect to the wifi downstairs I sometimes get excellent performance but it doesn't last long, slowing down to a crawl frequently, sometimes failing altogether and then a few minutes later it's back to normal for a while. The wireline connection status light is usually normal (green) downstairs but red or orange upstairs. It's never green upstairs.Both Zyxel units are plugged directly into wall sockets and I have experimented with different sockets for the downstairs one but without much benefit between one another. The unreliability experienced seems random, no particular time of day and no electrical items in our house seem to be switching on to cause the problem. If anyone has any suggestions for solving this problem I would be most grateful!

Ian

Have you checked performance when the units are close, i.e to rule out a dodgy device

Yes, in fact this evening I reset both adapters and reconfigured their network names and encryption and swapped them around in the same room. The units are very similar in characteristics.

I still have a pair of 200Mb D-Link adapters that the Zyxels replaced - I will try those again tomorrow. As I write this the Zyxels are 500Mb units and they are only managing 2Mb download from our Super Hub and we have 60Mb Virgin service,

Ian

I remember seeing similar issues elsewhere when I was looking for the latest version of the monitoring software, I think it was fixed with a firmware update.. Very vague I know but could be a starting point.