@Murdock73 

Hi,

If possible, connect yourself to the "Extender" via TP-Link's "tpPLC Utility" software. It could potentially have linked up with an unsecured Powerline adapter of a neighbor.

https://static.tp-link.com/res/down/doc/tpPLC_Utility_(for_Windows)_V1_UG.pdf

By the way, did you pair your two devices while they were plugged into wall sockets of the same room and once paired you brought one of them down to the garage? This is the recommended way.

  @woozle i'll try the pair at home and then downstairs, thanks. I'll let you know if it works

After the pairing at home, now the extender doesn't connect at all while in the garage

I don't think it's far then 300m maybe there are problems of interferences due to the great amount of electrical cables serving all the garage. 

There's something else i can try?