@rafafdez  Hello, 

From your information, the Powerline Led and Ethernet Led are OFF on the extender powerline unit right?

It is recommended to put 2 units in the same room and manually pair them againby pair button

Please refer to the instruction:
https://www.tp-link.com/support/faq/1081/

Note:  press Pair button only for 1 sec, Power Leds should be flashing on both powerline units in pairing process. ( if the Power Led does not blink, press it for 1 sec again)When the Powerline Led or House Leds are on, the pairing process is done.