Blue C Wire connected + Batteries and no power

[BCWhitemarsh]

Initially I had no problem with my thermostat (with blue wire in c slot) but later it said battery exhausted so I replaced them multiple times and yet it still says Battery exhausted and it’s getting no power.  

My other unit in the house doesn’t  have a blue wire and works fine.  I tried disconnecting the blue wire on the bad one to just use batteries, but it still says the batteries are exhausted and I know they are not. 

any ideas?

[jb76]

Hi - here is the standard 5-wire setup for a Nest Learning Thermostat (3rd generation):
W1 - White wire (usually) - Furnace/Heat control
Y1 - AC/Compressor control (usually yellow wire)
G - Unconditioned fan control (usually a green wire)
C - Common wire (usually blue wire) - carries 24V power back to Nest Thermostat.

Rh -Furnace power (usually a red wire)

Can you confirm the power levels going to the Nest Thermostat (Settings-->Equipment Info -->Power)?

*Critical things to note indicating enough power is getting to the thermostat - Power: Should be 3.85 V or higher and 'lin' mA(c) - should be 200 milliamps. If these power levels do not match, then the Nest is either not able to charge (bad battery) or the connections at that baseplate are not providing power via the C(common) wire and would require additional troubleshooting/HVAC tech. to review.

J

[zoeuvre]

Hi folks,

Thanks for chiming in, @jb76. 

@BCWhitemarsh, uh-oh! I'm sorry to hear that your Nest Thermostat still says no power though C wire is connected to it and you've already changed the batteries. Did you use a high-quality 1.5 V AAA alkaline batteries from Energizer? Also, follow these: 

1. If the display still turns on, gather the power readouts of your thermostat's VIN, IIN, PS-* under Settings > Equipment > Power. 
2. If you have a multimeter or voltmeter, use it to get the voltage reading of the C wire. 
   • Set the dial to 200 VAC.
     • If the multimeter doesn’t have a 200 setting, choose 100 or 250 VAC.
     • The general rule of thumb is don’t set it too high (500+) or too low (50). Place the red lead on the R wire.
   • Place the black lead on the C wire being tested.
   • The normal readout should be somewhere between 20 and 30 V (24 V is most common).

Let us know how it goes.

Best,

Zoe