We’ve updated the compatibility tool so there’s a note about C wire, but you’re right – it could be clearer.
I took a trip back through the compatibility wizard, and (unless there are more changes coming) it’s there but it’s still not obvious.
First, I tell it what I’ve got:
Then, it tells me what to expect:
I’m compatible, no reservations, it says. Unless I click through the “Learn more” link, which from the context sounds like it’s going to help me decide whether I can install it without help, not whether it’s compatible with my wiring. That link goes to a “Does Nest need a common wire?” article, which has some useful information, including recognition of the possible problem, a suggestion to do what I did (turn another wire into a C wire if possible), and a link to even more details.
That’s the right information, but I wouldn’t expect to find it hidden behind that “Learn more” link, and I still think anyone who clicks through the compatibility wizard without a C wire should see it. Maybe these problems are rarer than my small sample size indicates, but on the other hand, this “power stealing” problem doesn’t seem like an easy one.
C’mon, Nest — I like the product, and now that I’ve got mine working, I expect to remain a happy customer. But for an issue this subtle and important, I think you’d do well to err on the side of caution.