I have 4 BT White disc's, one plugged into my BT router (BT Broadband) by Ethernet, the other 3 scattered around the house. Recently the 3 have been unreliable, occasionally having no WiFi, turning red, etc. I decided to follow the instructions to add a new disc, and therefore plugged one of the 3 routers in to power, connected it by Ethernet to my router, turned it on and pressed the factory reset firmly for 2 seconds. Despite doing this, I keep receiving the "Unable to detect disc'. I repeated the exercise 2 further times with the other discs without success. What am I doing wrong?