Nest Thermostat Gen 3 Power issues

[Spots]

I have two Gen 3 thermostats in my house. My upstairs thermostat seems like it’s not getting power from the wall base and won’t stay charged, works perfectly fine if I move it downstairs (stays charged). Checked all connections with a multimeter and all connections are showing the correct voltage of either 240 or 24 respectively where they should. I did realize that my downstairs thermostat has 5 wires with the blue wire connecting at C. Upstairs thermostat only has 4 wires and nothing connected at the C input. Could this possibly be what’s wrong. Moved in 1.5yrs ago and it has worked fine this whole time but I’ve only started having power issues with the upstairs nest these past few weeks. Works fine if I switched the charged one from downstairs but quits obviously after it drains it’s internal charge. Any help or ideas would be greatly appreciated 

[HVAC]

If you don’t have a C wire connected then nest has been working off internal batteries all this time. Sometimes you have extra wires that are not exposed or wrapped up and pushed back into the wall just need to connect at nest & at upstairs air handler / heater circuit board. 

[Spots]

Thanks, I’ll pull off the Thermostat base tomorrow and see if they just didn’t connect or pull through the missing wire. Attaching pictures of both and maybe that might help someone help me. My electrician just thinks I either need to just replace the whole upstairs thermostat unit including the attachment point or it’s the transformer inside the upstairs HVAC unit going bad

 

 the bottom picture is the upstairs one 

[EdmondB]

Hello Spots,

Thanks for posting here in the Community. This is most likely a power sharing issue since when you move the upstairs Nest thermostat display works when you connect it to the downstairs thermostat base which has a common wire connected. If you don't have extra wires on the upstairs and don’t want to run a new wire, you can purchase a power connector and connect it to your HVAC.

Here is a link on how to install a power connector.
 

I appreciate the help, @HVAC.

Let me know if you have additional questions.

Best,
Edmon

[HVAC]

I can only see 4 wires on your upstairs can’t really zoom in all that much. If you can remove wires off & pull out if you have some slack try to strip some the outer plastic barrier back might be an extra wire in there. If it’s not too difficult you can just have electrician pull new set of wires and connect back same way just need to connect C to nest and your air handling equipment. you mentioned that you’re getting 24 volts so transformer is good. Good luck