When I connect the kit, there is no single from the extender unit. Both units are on the same circuit, and all the LEDs on the adapter initially light up, as do the power and and power line LEDs on the extender unit. One other thing: after about 10 minutes of two units being powered up, the powerline LEDs on both units switch off, even if the units are positioned directly next to each other in the same two-socket power supply.

I have upgraded the firmware, confirmed that the units are on the same electrical circuit, tried the extender unit in various sockets and reset the unit, but nothing seems to have worked. This is after a house move - the new house is a small, two-bed flat with very little distance (but also three walls) between the units. 

Any ideas what might be going wrong?