Two Nests...Two Generations...Two Low Batteries!
I'm at wits end today with my Nest Thermostats, and searched around to find a forum to seek help. I'm hoping I came to the right place!
I've had a 1st Generation Nest for about 5 months and have been very happy with it. It controlled my central AC without a hitch in late summer, and has been flawlessly operating my heat all winter.
I went and bought a 2nd Generation Nest unit about 3 months ago. I received it on launch day, and it's controlling a 2-wire heat-only system in a separate zone.
Both were working fine up until the last few days. It's been really cold here in the Northeast USA for about 10 days straight, and the 2nd Gen Nest unit started having intermittent problems. On two occasions, I noticed it was calling for heat (illuminated "orange"), but the zone valve was closed and there was no heat running to my baseboards. Both instances happened overnight after running for 22 or 23 hours straight, with only a few momentary on/off cycles. To correct the issue, I manually turned down the thermostat, waited 30 seconds, then cranked it back up...the value opened and heat starting flowing.
I called Nest and they have me monitoring my battery levels, concerned about if I'm getting a proper charge.
Fast-forward a few days, and I now have two Nest units that have chronically low batteries. Last night, both units were right around 3.70 volts, not connecting to Wifi, and had me worried about losing heat overnight. I disconnected both and charged them for an hour each via USB.
I plugged both in before bedtime, they connected quickly to Wifi, and they ran all night...except both reverted to "low battery" status around 4am. I'm checking now via the mobile app, and they are both off-line for 8 hours or more. Please note: Even though they charged for nearly an hour via USB, the batteries both still read below 3.8 Volts when I plugged them back into the base. But, since the Wifi feature was back and working, I figured the problem was temporarily solved.
Nest had me thinking there was insufficient voltage to feed the 2-wire system, even though it worked fine for 3 months. But, now, with the 1st Gen Nest having a battery issues as well (doesn't that draw power from the AC circuit?!), I'm concerned something else is going on.
As additional support, here's what my voltage readings were on the 2nd Generation Nest when I started having problems:
When calling for heat: 37 Voc, 7 Vin, 20 Lin
When at rest: 37 Voc, 35 Vin, 40 Lin
Hopefully someone on here can help point me in the right direction! I'm starting to freak out that I'm going to lose heat completely with a house full of a pregnant woman and toddlers! I just feel like I'm putting an awful lot of time and energy into this thing...I mean, it's just a thermostat, right?!?!
Thanks so much for your help
First off without a common wire connected to the Nest the only time the battery can charge is in standby (not calling for heat). Like a light switch, with the switch off you can read 120vac. across the two electrical connections, with the switch on no voltage reading. The extended run times during the colder weather may very well be draining the battery, the 7Vin with the heat on would be 35Vin if you had a common wire. As a test, for a few days till the weather moderates, I would disable the wifi and save some battery.
Yes, it's just a thermostat, and if you can find one that does what you want it to do without hassles, that's probably the way to go.
I'm not sure about the valve problem you described...I don't know if a fully charged battery would solve that or not, but I suspect those two problems could be unrelated.
Regarding the battery level, I've seen quite a few posts like yours (here and elsewhere) from Nest owners who either don't have or didn't connect the 24V common 'C' wire. I suspect Nest has oversold their claim that the thermostat doesn't need it. After reading quite a bit before getting Nest, I found that my thermostat wiring had an unused blue wire. I hooked it up to 'C' on both the furnace and the Nest when I first installed the thermostat, and I have not had any problems at all so far. When I look under Settings/Technical Info and look at the battery voltage, it always says 3.93 volts. I haven't seen it deviate from that value at all.
If I were having the problems you've described, I would first check to see if there is any way to connect a 'C' wire. If not, I would probably return the Nest and look for another solution. But I'm not an expert in this stuff--that's just my (mostly uninformed) opinion.
Nest Power Issues
I have several Nest thermostats installed. I would recommend that you always install the common wire. If you do not and your furnace runs most of the time due to cold weather, the Nest battery will go dead. If the furnace only comes on 50% of the time and perhaps more there is no problem with the battery going dead without the common wire. It is pretty easy to install the common wire providing you have the extra wire in the bundle going from the thermostat to the furnace. If not it is a bit more of a hassle.
Originally Posted by harrv