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Nest Thermostat not holding a charge

Community Member

I have 3 Nest Learning Thermostats, all 3rd Generation wired exactly the same way, 2 function normally 1 is not charging.
I have had the Thermostats for about a year and 1 has recently stopped charging. We manually charge the unit by plugging in the USB port on device, then restore unit to the base.
This unit is connected to a Base Board heating system using the Rh - W1 24 VAC wires. It is also connected to a separate cooling system using the Rc-Y1-G 24 VAC wires.

Current relevant settings on all thermostats:
Settings menu
- Equipment
Base plate diagram displayed with message "Equipment detected" showing Y1 - G - Rc on left side and W1 - Rh on right side.
select continue
Display now shows "N72 wiring Report. Power wire Rh detected. No connection to equipment. more info at ..."
Select menu option Tech info - Equipment
Displays "Equipment sensed on W1-Y1-G-Rc"
The power menu has the following values: Battery: 3.632v; VOC: 38.21v; Vin 36.14v; lin: 40 ma(i)

All thermostats operate the heating and cooling functions properly. So the all thermostats are operating the heat properly over the Rh-W1 wires, even though the message indicates "Power wire Rh detected. No connection to equipment"

Both heating and cooling systems do not have a control board (as shown in all DYI help videos), they wire directly to the controlling switches inside the units.

I would like to try to set up a C wire on the thermostat to enable constant charging, however I am not sure which 24 VAC system to run the common wire to. since there are 2 different 24 VAC systems. It does appear that the system is using the Rc wire for whatever power it gains, so I was contemplating returning the C wire to the AC unit



Community Member

This is exactly what I ended up doing: running a C wire back because of the same issue you're having (if you have not yet, try searching for "power stealing" to see how the system works - but I suspect you already know).

It seems to me (just Joe Homeowner; a skilled layperson) that the "common" way to do this is to run a c wire back to the cooling system. That is what I did and it resolved my problem.

One cautionary note - very much secondary to this, but related: everything seemed fine for me over the summer, I even tested the heat, but come ACTUAL heating season in the northeastern United States (November for me, this year), the heat wouldn't kick on, and I found a new N72 error. That is actually why I'm on the forums right now after a few weeks of troubleshooting. I think that issue is NOT related to the choice of equipment for Common, because I actually ran yet another common back to the aquastat a few hours ago and it did not improve anything.

See this link (Nest Thermostat Error N72) if curious, and good luck! Hope your air handler internals are not as much of a rat's nest as mine were (pretty much normal for those of us who do not have some kind of control board in there).

Community Member

I have 3 Nest 3rd. generation learning thermostats in my house connected to a single boiler with radiant baseboard heat; the boiler also heats our water tank for the entire household hot water.  My Nest thermostats were disconnecting from my network because the back-up battery on all 3 of my Nest thermostats were discharging. 

THE SOLOUTION:  I had my boiler serviced recently, and my boiler technician told me that I only had one 24 volt transformer that was supporting not only the 3 Nest thermostats, but also 3 other accessories attached to my boiler.  He replaced the old 24 volt transformer (it can fit in the palm of your hand it's so small) and installed a second 24 volt transformer on the wall next to our Weil-McClain boiler that then split the 6 accessories with 3 each being supported by its own transformer.  That fixed my problem!  I no longer get my Nest thermostats disconnecting from my network because the battery has discharged.  I'm back to the normal Nest thermostats that I didn't have to worry about.