Help Connecting Nest Thermostat to Network

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So I have a Nest thermostat which was connected to my network fine through my Fritz!Box. However, this weekend I installed some powerline/wi-fi extenders (TL-WPA4220 KIT) and moved my router. Since doing so I can no longer get my Nest Thermostat to connect.

The only way I have solved this is to turn off all security on my router and connect, however as soon as I turn the security back on the Thermostat disconnects.

Any help/advice would be appreciated.

 

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Hi all, sorry, completely forgot about this post. We actually have an electrician in doing some work at the moment and he had all the power off for a few hours recently, once it was all turned back on I noticed the Nest Thermostat connected back to my network completely fine without me having to do anything. Maybe the router or the Thermostat just needed a solid reboot to get it all connecting again?!