I wanted to let others know about a problem and how to fix it! My furnace was having trouble starting up. It would sometimes try to start, not ignite, and stop for up to 20 minutes. Had NO IDEA it was related to my Google Nest. Then, on the coldest night of the year so far, heater took 5 hours to come on! When the technician came, he noticed I had a Nest. He asked me if the C wire was connected. The what? Lol!
Anyway, it was NOT connected and he said that he has seen this issue many times. In layman's terms, if the C wire isn't connected, the Furnace gets confused. In the Nest instructions, I believe it says the C wire is not necessary, but in my case it was very necessary.
He connected the wire, and all is well!