E448 No power. Switch from Honeywell to Google Nest

[louis8542]

Hi All,

I recently changed the thermostat from Honeywell to Google Nest, however, after wiring everything up, I got the error message that shows no power. Attached are the current photos of the wire from the Google Nest and the furnace control board. Troubleshooting with many online instructions, but none of them work.

Please guide me to properly resolve the issue, thanks.

Old Honeywell connects to R, W, G and Y.

https://photos.app.goo.gl/UbjTPNFXFr26XasF8

[ODgreen]

I had this issue with my old furnace. You aren't getting a constant stream of power from a C wire so it is only charging the internal battery when heating or cooling. Three options to fix. 1. If you have an unused wire, attach it to C on the thermostat side and the other side to the low voltage power terminal on your HVAC board. 2. If you don't have any spare wires, Google sells a smart adapter that connects to your HVAC board and makes it act like you have another wire (this is what I did and it worked great). 3. If you can access your whole thermostat cable, you can replace it with one with more conductors to get a dedicated power line. When we upgraded to a heat pump, we also upgraded this cable and are still using the same Nest thermostat. Good luck 🤞

[Patrick_Caezza]

@louis8542 

Do you happen to have a picture of the original thermostat's wiring?

I'm having trouble identifying the control board terminal strip. Does the Red wire connect to a separate wire, rather than the terminal block?

Can you post a better picture of the control board terminal block?

[louis8542]

Thanks for all the assistance. I used the Nest power connector to power on the Nest.

However, a new issue has occurred. When the cooling request is sent to the furnace, the device runs but has no cooling functions. I might have missed the key step in properly sending the cooling request to the condenser. 

And there is no issue with heating, everything runs well. @Patrick_Caezza 

[ODgreen]

Sounds like a wiring configuration mismatch or bad connection. Calling the nest thermostat help line is probably the fastest way to walkthrough troubleshooting. I had to call them at some point and they were very fast, friendly, knowledgeable, and free.

[louis8542 · Accepted solution]

Thank you! I called the tech support to resolve the issue. It turned out that the auto schedule overwrites the current temperature setting. Once I removed the schedule, the system returned to normal. It's a huge relief. 

[ODgreen]

Congrats on solving your issue! Hopefully it brings you many years of comfort and savings. It was my first foundation piece of smart home devices and it's pretty neat to see how much they work together.