A couple weeks ago I ran into an issue where I discovered the battery inside my old thermostat had split open causing a mess, the reason I noticed was that right around that time the fuse had blown on the system. I replaced the fuse and everything has been good since, heating and cooling without issue. Here is that original thread, in case it helps with any information.

However, since the old thermostat was not programmable and Nest were releasing a new $129 thermostat I decided to upgrade the thermostat. After waiting a few days for a trim plate to arrive I installed the unit today. While I had some initial confusion with the wire locations (I was reading the conventional labels on my set up, not the Heat Pump labels) I mounted the Nest on the wall, connected all the wires and started the set up. It initially reported an issue with the W wire, so I shut the power off, removed and re-inserted the wire and it then seemed to continue on with the set up. At this point, I set it to cooling and the system started up, so far, so good.

A few minutes later, I felt the air coming out of the vent and find that it is warm. Double checked the thermostat is set to cool (internal temp showing 77F, thermostat set to 74F and blue background indicating cooling). Digging into it a little more, I see it showing a system error which turns out to be that the W wire is not detected still. After removing, reinserting, cutting the old end off and stripping the wire to a new clean end, it still fails to detect the W (or AUX) wire.

At that point, rather than the house just slowly heat up, and to rule out the system being an issue, I re-installed the old thermostat. Without knowing exactly what the W wire is for (looks to be controlling the heat, but not sure exactly which part), the system is cooling as it should be, so on that point the Nest was having issues as it was blowing warm air. I am not sure if there is a test I can perform on the W wire to rule any issues out there. Here is a picture of the existing thermostat wiring:



As well as an image of how Nest said I should wire the new thermostat (the image shows a Nest Thermostat E base plate, but the base plate on the new thermostat is very similar with just 6 wires):



The system is about a decade old, Trane XR13 outdoor unit, 2TGB indoor unit.

Thank you.

 

Did you set the nest to heat pump with backup heat ?
Verify that the * O/B is set to O for cooling.

When in programming for a heat pump.... you must tell it single fuel.
The nest will then know that the W1 wire is aux heat.

 

I didn't see anywhere in the nest set up to set either heat pump with back up, or *O/B as cooling. Not sure if that's available on this version, although I would assume it must be somewhere. I'll dig through the settings, the manuals as expected, mostly useless.

Edited to add, I went through all the settings on the thermostat, there are none to indicate heat pump with backup or set *O/B. I've seen those settings mentioned on the nest learning thermostat, but do not see them on this new, non learning one.

Just to test, with the old thermostat cooling, heat, heat with aux heating and emergency heat all working fine.

 

Is there an exact model number on that stat ?
The market is very confused with multiple versions of the same model.

 

Yep, it's a G4CVZ. Just released on i think 20th Oct.

 

I'm looking for technical information.
Hopefully you used the compatibility system and it's compatible with your system.

 

Yep, used the compatability checker and also used Google chat support earlier when I was not certain on where to put the orange and white wires, they asked for model number of hvac unit and thermostat and verified its compatible.

 

You're going to have to look for online programming if they haven't given you written instructions.
I'm reading confusing connection reviews on that stat. Says needs a C wire and then needs AAA batteries ??

The nest E was programmable by turning the temperature ring on first power up,

 

I think that the Nest Learning thermostat is also programmable in the same way as the E. This has no ring, but a touch slider on the side. Included documentation is minimal at best, I'll hunt around to see what I can find. I have a C wire and the thing came with batteries.

 

The nest E programs by turning the round front ring to select function.
I have that programming and the pro programming.

I'm still looking.

 

Thank you...

I posted this at the reddit nest forum and think I may have an answer...

"For the new thermostat you need to enter the correct wiring in the screen that says something like "What wires do you have?". In your case you need to check R,W,Y,G,C,O/B. You may need to factory reset the device to restart setup and enter these wires."

I'm confident that I selected the wires based on the conventional set up and not a heat pump, aka wrong. While I'd love to try this now, I'm beat from a 5am meeting at work, so it will have to wait until tomorrow. I'll make shut to reply here regardless of the outcome, but hoping this will resolve things.

 

Reset the unit and re-wired it, it actually asked me a bunch of different questions this time, such as is it a dual fuel set up, setting either the O or B wire for cooling etc. Initially it reported no wires were connected, but that appears to just be that it was not fully seated due to the wires poking out from the wall just blocking it from seating fully.

Turned on cooling and it started blowing cold air as expected. It says something about a system error, but when I went into the menu where previously it was showing the W wire not connected, there is nothing. Just an exclamation mark next to the emergency heat option. I have not yet tested the heating, but I will do that shortly and then see if I can figure out the last error. Fingers crossed though it should be working.

 

Possibly the wire is not installed all the way.

 

Dang it, looks like it is still the W wire that is causing issues. It's seated fully, the wire itself is clean (I cut a new end on it). Is there a way to test the W wire functionality? Looks like that is for the AUX heating, which was working with the old thermostat when I ran through the settings with it yesterday to make sure everything was still working.

Assuming that W / AUX is for the auxiliary heat, is it worth turning the nest to heat cycle and turn up the temp such that the system should switch on the auxiliary heat?

 

During the original startup.... it should have asked dual fuel or single. You would have needed to pick single fuel. That is supposed to tell the stat that the W wire is AUX heat.

You try setting the thermostat up but if it says no wire on W..... most likely the aux won't start.

 

I picked single fuel during set up, might try resetting and set up again, maybe take pictures of the set up along the way.

So, if I leave it saying the W wire is not connected, heat will work, just not AUX heat? If so, that at least gives me a little time to research and try to figure out the problem.

 

I have a brand new house that I am trying to turn into a smarthome but I've hit some hurdles this being one

 

I did figure it out, but to be honest it sort of did it on its own. I think I reset the unit, took it off and put it back on the base and it's been fine detecting all the wires and working well since.

The only issue I get is that it sometimes thinks no one is home, when someone is home.