E79 error

[VernJ]

we have had our Nest for a year at the cabin and it has worked prefect, I opened the app today and it tells me we have a E79 error. 

We where at the cabin last week and everything was working. what should a be looking in to? i see lost of video's on new installs and getting the E79 but ours has been working good for a year after the contractor installed it  

[BinaryJay]

E9, E29, E79 and E159

No power to C wire detected.

It appears that the cabin has lost power, or the equipment that it's connected to has stopped providing power to it for some reason.  Basically, as best as we can tell just from the error alone it's a physical problem with the power.

[VernJ]

Thank you , I am going out this evening I will see. 

[Nestoldum]

Hi, I have the same issue after 3 years of smooth operation. "Rh is physically recognized but not electrically" is where I am now. Rh is shown on equipment screen but grayed out. I even installed nest power connector and now I have 24V but still not charging. Heating works somehow. Any advise is appreciated.

[Jake]

Hey All,

I am sorry for the delayed reply, and to hear about the trouble you are running into. I wanted to follow up and ensure you are good to go. Please let me know if you have any questions from here, as I would be happy to take a closer look and assist you further. 

Best regards,
Jake

[Nestoldum]

Hi @Jake, 

So I have had Nest learning thermostat properly working for 3 years. And now it does not charge itself. I have 24V checked with a meter, even installed the nest power connector to boiler to see if that helps without any luck. The only issue I can get from Thermostat is the Rh wire is being grayed out and the associated error message N72, "Rh wire detected, no connection to equipment". However if I set the thermostat to higher temperature, heating system works just fine. So for whatever reason the Rh wire is sending the signal but failing to receive to charge the instrument. I'll be happy to troubleshoot if you have any ideas. Thanks

[Jake]

Hey Nestoldum,

Having the device not charge is never ideal, let's jump in and see if we can isolate the trouble. If you are seeing an error code "N72", this means that the device is having trouble detecting the RH wire.

Do you mind me asking, have you restriped the wire recently, and ensured it is securely in the device? Are you able to review the wires the device is showing registered? If you are thinking it could have something to do with the HVAC system itself, I would recommend having a Nest Pro come out and take a closer look at the system. They would be able to isolate the issue, and ensure everything is working properly. 

Best regards,

Jake

[Nestoldum]

Yes I made sure the Rh is properly in there. Actually i even tried connecting rh and w into rc and y. And the system works fine, except that it thinks it is cooling. Anyway, i connected my nest E thermostat leaving the ac cable out and that way system also works fine. So error only happens when both ac and heating is connected. But these used work fine for 4 years and suddenly have this issue. Anymore advise is appreciated but i guess i’ll just switch to another brand rather than paying nest pro hundreds of dolars. 

[GarrettDS]

Hey there,
Just wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Best regards,
Garrett DS

[GarthC]

My nest 3 says no powers to blue common wire. If I disconnect the blue c. The thermostat works but AC switches off. If I connect the blue C wire it works great and blows cool. Just the nest thermostat does not work. Says wiring error now power to c 

[Rwstevens]

I just started having this problem today the system is running but I'm getting the e79 error code and it's saying no power to my c wire anyone have a fix to this?

[GarthC]

Turned out I had to connect the blue wire to the thermostat. And go to the unit and connect it. Apparently solar companies disconnect the blue wire. Now everything works great 

[Nestoldum · Accepted solution]

Hi everyone, after about 2 years of Nest issues, I finally solved the issue by converting G wire into a C wire. Although I was already measuring >24V without this conversion (and it worked for 3-4 years without issues) it seems it now needs this C wire. It wasn't easy to figure out how to make the conversion on the air handler side which includes figuring out which wire goes to thermostat and to compressor and figuring out the jumper wire situation. But at the end it worked out. I already got an EcoBee and its manual actually helped me a lot more than Nest/Google people. So if people with heating/cooling two separate units having all of a sudden this N72 (or whichever error) that runs the battery off of your Nest not so smart thermostat, then definitely consider i) G to C conversion, ii) run a C wire, iii) install the power adapter. Good luck!

[Jhonleanmel]

Hi everyone,

@Nestoldum, we appreciate your helpful response ― this really helps the community a lot.

Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

[EdwardT]

Hi folks,

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

Thanks,

Edward

[EdwardT]

Hi folks,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.
 

Thanks,

Edward