It's been up for 120 hours now and not one instance of a dropped network link. The irony here is that the range of the BT SH2 is so good that the Powerline adaptors are no longer essential.

There has been an unexpected conclusion to this issue that I am posting for the benefit of others. I spent £18 on ebay to obtain a brand-new BT SmartHub 2 with the intention of checking how it will...

Thank you, @Joseph-TP I've updated the firmware by a couple of years 2014 to 2016, lowered the peak bandwidth from "games" to "video" and moved the devices closer. Will see how this affects...

@Gerryatrix said Upgraded firmware on the repeaters to WPA4220(UK)1.2_update_1.2.9_20160525 (was 2014 V1) You never know, maybe this will help matters...

Currently using two AV500 powerline wi-fi extenders with their base unit connected to BT Smarthub via RJ45 ethernet. Mostly this setup works well. The VDSL and main wifi network is 99.999% reliable...