Nest basically says you don't need a C wire, but if you have any problems, use a C wire. Wow.
Was anybody are of this Nest issue? I did not have a C wire and my fan was intermittently coming on for no reason. Added the C wire, problem fixed.
Got nowhere, could not get past first level Nest support who I suspect know nothing about this. Link below is one explanation of how C wire circuit works.
https://marco.org/2011/12/17/nest-incompatibility-without-c-wire
