It does not work! it just cycles the heater on/off.

Nest TS think the HVAC system is to blame. Any thoughts?

there is an addition with a separate HVAC system and the nest thermostat in that area works perfectly! I know the bare minimum about HVAC systems, Voltage should be on the W wire? correct?

I feel your pain.
I was so pumped to get mine up and running. I ripped my Prodigy T-Stat down, and got to it.
It calls for A/C if I request heat or A/C. I haven't had a chance to call TS, but I triple checked wiring, watched their you tube vid, nata.
I put my Prodigy back, and everything works fine.
The funny thing is, I put 2 in this week at clients houses, and they worked perfectly. I guess if it's gonna break balls, It's better at home.
JT

The real question is why get rid of a real thermostat with integration capabilities only to put in a fancy stupid not integratable thermostat?

I'm a CI. Like most of us, my house is the guinea pig for most of the products I decide to carry (or not). If you saw my current setup, you would crack up. Prodigy for climate, 1 room media room and 4 zones of audio, Crestron MC3 for another media room, Sonos for my outdoor, 2 ProControl R's for TV rooms, and much more crap.
For the client that buys Sonos, The Nest is an easy sell.
Would I rather sell them a Crestron system and integrate everything? Yup.

JT

We tried these on 2 installs and they have given us nothing but trouble. Voltage dropping and draining the battery, heat being turned on when one calls for a/c. This is even after nest sent a HVAC tech to fix the issues (which they paid for). No more nest for us, too much trouble and we make nothing on them.

I've had a Nest in long-term testing since last summer (review soon) on a Trane dual-stage furnace and A/C, and so far it's been trouble-free.

If heat is cycling on and off, chances are it's an issue with how the unit steals power from the heating circuit to charge its battery. The typical solution to that is to feed the Nest with a dedicated power connection from the furnace (just requires a cable with enough conductors).

Interesting....I've had 4 nest units in a home since last june, working fine.
I signed up for the beta program and they sent me a free unit, refurb. There was nothing but problems..basically worked fine for a few minutes then turned on heat. Every time. I figured it was a bad refurb, finally ripped it out.

I have 4 more units specified to go into a home in june...maybe I should rethink that

For a 2 wire heating system the R wire should have 24 volts on it always. The W wire is call for heat wire so it only has voltage on it when itrequests heat.

We need more info on your setup. 

As for voltage drops hooking up the C wire to the common on the board should resolve those issues.

Yeah, don't ever use power stealing if you can avoid it at all. Always have a separate 24V source of constant power. You can even power from a completely separate 24VAC transformer if you need to (and have extra conductors at the stat and know what you are doing).

It's crazy how hard it is to wrap your head around HVAC controls in this industry. Out of everything we do, 95% of these things are just power and relay wires. You'd think it would be a no-brainer for us. It took a LOT of thinking before it clicked for me...

I call my hvac guy before I do anything with stats. I put a prodigy tstat into a condo, it was a heat pump so I wired it as such.

The issue I had was that even though it was a traditional pump, it only used emergency heat due to it being in a small condo. I had no way of knowing this, burned up a relay, made a mess.

I'm really not qualified to mess with hvac, if there is a problem I have no way to fix it, and there are so many types of systems out there that I don't know enough to know what I'm doing, only enough to be dangerous.

Then the problem arises if there is a problem, the hvac guy says its not his stat so not his problem. Then add in that there is a touch panel integrated with it, it will blow the hvac guys mind.

My best practice is to have the pro hook up the stat and then communicate with it.

HVAC wiring seems excessively complex and archaic compared to what would actually be needed with today's technology (hello CAT5 + POE). Have you seen the Trane dealer instructions on how to wire their furnaces for different fan speeds? It's like a mathematical logic puzzle designed by the Russians to occupy the American scientists during the cold war...

+1
If you can't find a spare conductor in the jacket that can be used for the Common power it separately. It's a totally different animal than a dumb White/Rogers or Honeywell.

Oh, and another thing to consider when swapping tstats in a customer's home. You may now own every HVAC issue they have. We just swapped tstats in a home and we found out after the fact that there were some issues in how the entire system was designed - some rooms got hot really fast, others not fast enough, etc. (to be clear, these were airflow issues, not thermostat issues) As soon as we had an issue with one of our new tstats, it instantly became this vague "cloud" of HVAC problems, and it didn't matter whose fault it was....we were involved either way.

So a big +1 for handing it off to an HVAC contractor, then just setting up the integration once they are 100% complete on their end.

+100% We have installed a few TSTATS in the past and have wound up owning some problems (understatement).

After thinking about it, I came to this conclusion: "why should I install (or worse actually promote TSTATS)?" Seriously, unless a client forces you to do this work, why would you want to take on this responsibility? It's not the money, there is not enough profit on a whole house full of TSTAT hardware and the associated labor to make up for one after hours call trying to diagnose an HVAC problem.

Bottom line (for me anyway): Is there any money in TSATS - no. Will I loose an otherwise good project if I don't bring up TSATS - no. Then why do I want the headache?

My 2 cents.

Im running out the door so ill comment more tonight but im not the one installing the T-Stat, the GC is. Im working on a small retrofit at a shorehome that isnt getting any automation. clients wanted something they could remote into to adjust the T-Stat and i mentioned the nest to the GC and he forwarded that onto the clients. They loved the Idea so he got two of them and because he's a good guy and spent hours with tech support i offered to find out if you guys had any incite to the issue.

ill comment on this more tonight! thanks guys!

BTW, i was looking into offering nest T-Stat but after this issue with them i have no care to offer them and own the HVAC system!