I have two Nest Learning Thermostat at home. One of them suddenly can't connect to the wifi network. it has the reported "w5 error". It does not even detect the WiFi. Have tried all suggestions: restart and reset both the router and Nest Thermostat. It still can't find the WiFi network.
The other nest thermostat and other devices have NO wifi connection issue.
Same issue here. Google support determined that my thermostat is "broken" and now I'll have to buy a new one. Pretty ridiculous that they won't stand behind their products or offer any type of replacement discount due to their products failing.
Now I regret spending all that money on google cams, etc. Hopefully they last more than a few years...