After years of faultless service the powerlines stopped talking today.

The following has started happening to both units on the same day. 
Every four seconds the leds go out. Then all light up, go out, then just the ones that should be on i.e. power and connected network light up. Then four seconds later the cycle starts again. 

Tried pressing pair button for 10 seconds. Tried plugging in next to each other. Tried leaving them unplugged for several hours. 
Are they dead?