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Nest 3rd generation thermostats losing power

Cip54
Community Member

I’ve posted elsewhere under the N72 posts. I have 4 learning thermostats. My HVAC system has three air handlers for A/C and 5 zones (Honeywell valves) for hot water baseboard heating.

One Nest is on a heat only zone. One is on an A/C only zone. The other 2 cover both heat and A/C.

Everything works properly in terms of heating and cooling, although both of the dual nests have an N72 error and greyed out Rh wire. However, all of the Nests started dying this spring, except the heat only device.

After much trial and error, I has a Nest pro install power adapters in my 3 air handlers. Unfortunately, the learning Nest doesn’t recognize the adapters in their software so can’t tell if they are working. Only assume as much since the A/C still work properly. 

For the heck of it, I replaced the battery in the thermostat that was dying most often. The only replacement I could find is rated at 1.4 mA instead of the 2.1 mA I replaced. It worked properly but loses power even faster than the dying Nests, so I assume the capacity is inadequate.

My 3 remaining Nests continue to require recharging, although less often. The Nest pro suggested that 3 years of use without a C wire has damaged the batteries due to overcycling. Nest customer support claims that if the Nest can charge the battery is ok.

So what is my solution? I can’t count on charging the things since I am out I would have no heat. I know I can switch the G to C but that is not a satisfactory answer since I run the fan by itself now and then.

I purchased 2 new Nests of the same vintage at a discount from my electric company and will replace 2 of the problem stats. If the battery cycling was the issue I expect the new ones should work fine with the power adapters. I also bought a FAST-STAT common maker for the heat only location to see if that works.

It is absurd that a premium product such as this would not work properly as advertised.

Anyone have a solution I haven’t tried? 

3 REPLIES 3

Markjosephp
Community Specialist
Community Specialist

Hi Cip54,

 

Thanks for letting us know. It helps us to isolate on what could've caused this. A few questions: 

 

  • Are all your Nest Thermostat devices are the same versions?
  • When was the Nest Power Adapters installed? 
  • How are your new Nest Thermostats? Do you experience the same problem?

 

Keep us on the loop.

 

Regards,

Mark

All four of my original Nests are the 3rd gen learning and were installed at the same time.

Power adapters installed in august.

haven’t installed the new ones yet.

Cip54
Community Member

Update 10/1.

installed the Fast-Stat common maker on one of my heat only zones. This Nest is the one I replaced the battery in. Installation was straightforward and my Nest now sees equipment on Rh, W and C. Everything looks good so far, sensing 24VAC and operating the Furnace properly. Battery power at 3.88 V

The three Nests running off the Nest power adapter are running well. Oddly, the N72 error is gone on both of the dual purpose (heat and AC) has disappeared. Wiring diagram shows power on Rh when it used to be grayed out. I haven’t done anything to those two Nests. Has there been a software update in the last few days?