Rh wire shows no power E448

[mdangio]

I have a heat pump system (B orientation as it’s a Freidrich/Rheem). I have a basic thermostat (Emerson brand) and it works completely fine. AA batteries power the tstat itself. It Heats and cools the house with no problem. Wiring for the Emerson is R, Y, O/B, G and E.

Nest app says to map the wiring in the following way:

R->Rh Y->Y1, O/B->OB G->G and E->*

When I go through the set up, the nest thermostat display doesn’t turn on when I flip the breaker back on at the electrical panel. I charged the thermostat and plugged it into the base. It detected all the wiring but underneath Rh it shows No power and gives me E448 as the error code.

I was under the impression I got a bad unit because my emerson tstat works fine with the wiring. So I returned it and got a brand new one and same issue. How can I ensure Rh is getting power?

[Redsquare]

I have the same issue after ten years of using second generation nest seamlessly. I bought new one after old one started showing no power error code. The same thing is happening. I had hvac person inspect the unit (regular force air electric) and nest pro fixing and reinstalling thermostat. Today it is offline again with “no power” code. What the hell is happening? Can’t find any answers maybe contacting nest again is the way to go. Any ideas?

[mdangio]

No idea so far. Created this post to get help. Hoping someone knows the answer. Might have to get an hvac or nest pro out

[Redsquare]

This might help. Today we tested power coming from all thermostat wires -dead. Then we uncovered hvac unit cover and tested the panel and all checks out. Flame sensor and the fuse were good. However, this only can be detected when thermostat is dead so no power to it. It randomly would turn on and off unpredictable though. So there is a safety button that gets depressed once panel is closed on the hvac unit. In my case it looks like over the years either cover isn’t as firm or the button is faulty, the thermostat kicks in and out once in a while. So this caused by that darn safety button that once panel is off the unit the power is off the panel inside. So solved here. Hopefully you’ll get yours figured out.  

[mdangio]

Thanks I took the panel of the air handler off and reseated it already. No issues there. System is also brand new

[Redsquare]

One last update. After all it was not a safety switch. The technician looked at the back of the control board and one of the metal points was partially damaged apparently to vibration over the years by not enough to completely be out service. Very bizarre. Hvac was on and off randomly. Not a thermostat issue! He did solder that point and that hopefully fixed the issue all together. 

[mdangio]

Decided to get a nest pro out to my location this weekend. Will update based on what happens

[kcruzgonzalez]

Hello mdangio,

Thanks for reaching out to the Nest Community! We're happy to help you with your thermostat wiring questions.

Thank you for providing the details so far and for contacting us for assistance. To give you the most accurate guidance, could you please share some photos with us? Specifically, we'd appreciate it if you could provide clear pictures of both your current Nest Thermostat wiring and the wiring configuration of your previous thermostat. This will allow us to compare the setups and identify any potential discrepancies or issues.

You should see a camera icon or an "Insert photos" option that you can use to attach the images. If you're having trouble finding this option on your mobile device, please try using a different web browser or a computer to upload the photos.

We look forward to seeing the wiring and helping you get your thermostat set up correctly!

Regards,

Kevin

[mdangio · Accepted solution]

SOLVED:

Decided to have a nest pro come out. She said it needed a C wire. I ran the c wire to the tstat from the air handler and it worked like a charm. My C wire was actually connected at the board on the air handler already but was tied off in a wire nut. I took some new tstat wire, connected it to the wire nut, ran it to the tstat and it works perfectly fine now.