Hello again, this is a follow-up as the forum won't let me add to my earlier comment so i am back in this way. I had an issue with 3 nest stats and i have finally found MY problem and perhaps some other folks problem as well. I installed my neighbour's stat a few weeks ago and we kept getting the "no 24 volt" error. I am a licensed electrician and have wired hundreds of stats so i was trying everything. Yesterday i retrieved his new unused stat for one more hail Mary and removed the batteries to clear any memory then used my test bench to simulate furnace power as well as a heat load and the stat worked perfectly!! I went over to his house and reinstalled it and got the no power error. I then did the wiring test and it also showed no w and y connected so i removed the stat and started looking at the push in terminals more closely!! The push tabs on several of the terminals were not all lined up so i removed all the wires and used needle nose to insert them in a way that made the push tabs depress (this took several attempts as sometimes the wire insertion did not do that, as if the wire doesnt always find the right spot). I tried by depressing the tab while inserting the wire and also by letting the wire do the depressing with the same results. Once i made sure the wires were in and seated properly, the stat worked perfectly!! I came home and pulled my stat and found one wire also not seated but it had been making enough contact to work. Part of the problem is when you push the bundle back into the wall after installation, it changes the angle and stress on the 18 gauge wire and may cause the open circuit condition. So botton line is after the final base wiring, check all wired terminal push tabs to make sure they are all depressed and in line, before snapping the thermostat on. I have never had that problem with screw terminals, but lesson learned and i am amazed that i do not see this mentioned in the forums...maybe i missed it!! Hope this can be of some help to somebody.
