E74 error no power to Rh wire

[Danjoyce1]

I installed a Nest learning thermostat about six months ago, which worked fine with no issues. About two weeks ago, my temperature sensor went offline and wouldn’t reconnect. Then the Nest app disconnected and wouldn’t reconnect, and then the wifi wouldn’t connect to the app, I get an E5 error.  I went on vacation for a week and and came back a couple days ago to the thermostat with a dead battery. I charged it with a USB cable and reinstalled it, which worked for a few hours before it died again. I bought and installed a Nest power connector yesterday. When I turned the power on, the Nest said there was no signal from the Rh wire. I uninstalled the power connector and returned it to the original settings, but still got the E74 Rh error. I realized the cover and safety switch on the furnace was open, but I reinstalled the cover and have the same issue. I called Nest support when the wifi wouldn’t connect and they’re sending me a new thermostat, but it seems like a power issue rather than a device issue, so that likely won’t be a solution. In the meantime, I have no AC in the summer heat. Appreciate any suggestions.

[HVAC]

If you're always charging nest then you DONT have 24 volts power direct all the time. Most of the time it’s the C wire that’s missing. 
You can alway work AC system with out a stat by putting proper colored wires together. More important than the colors are the imprinted LETTERS on the mounting plate. R G Y good luck 

[Danjoyce1]

Thank you. I never had to charge the Nest during the first 6-7 months of owning it, only in the last week. I think there’s an issue with our wiring which I haven’t been able to identify or fix. There’s no C wire but I understood the Nest should work without it, and it had been up until recently. I’m linking to photos of our wiring here: https://photos.google.com/share/AF1QipOWvvz3Pm7T5VvvvHUHJJT-4vBJ2-nJx5CqT6nNnoDlMbmZ5MTLfllLenaKJ6l7...

[HVAC]

I see the yellow wire that’s connected to Y on nest goes to a black wire to the left of the board and another black wire comes back to the board to Y terminal. That means you have an external protection switch possibly a back up drain float switch or other safety switch of sort. If the AC works after you charge the nest then that switch is ok otherwise might need to address that switch issue. Now you can use the green wire connected to G on nest and board &  connected to to C on both nest and board but you would need to add a wire in between G & Y on the board to have the fan come on when the AC comes on. You would lose ability to turn on the fan ONLY option. Nest will recognize that and fan only option would not be visible on the nest. Hope that helps good luck. Remember alway disconnect power before working on it. 

[zoeuvre]

Hi folks,

@Danjoyce1, thanks for reaching out to us, and I'm sorry to hear about the situation. Let's sort this out.

Please gather the power readings of your Nest Learning Thermostat on its Settings > Technical Info > Power (Battery, VOC, VIN, and lIN). 

I'll look forward to your response. 

I appreciate your help, @HVAC. 

Best,

Zoe 

[Danjoyce1]

I couldn’t keep troubleshooting with no AC so I ended up calling an HVAC technician who ran a C wire to the thermostat. It’s working fine now. I returned the Power Connector. Thanks for the advice.

[Jenelyn_O]

Hi Danjoyce1,

Thanks for keeping us in the loop. I'm glad to hear that it's already fixed. Please feel free to create a new thread if you have any questions or concerns in the future, as we'll be willing to assist you. 

I appreciate the help, @HVAC and Zoe.

Cheers,

Jenelyn