Nest Thermostat having M25 code

[Pkgupta]

Hi,

We installed two Nest Thermostat regular with C wire on two different floors. Checked that all the 5 Wires (Y-C-W-G-R) detected on Thermostat and App both. Tested the terminals between R and C before installation and found 27.4 volt coming. But if we go to: Equipment -> Power Connector -> Power Status

It show "Power Test Not Run" and "g.co/nest/m25". So we tried to run Power Test, and nothing happens and still shows the same thing. We go to that link, and it says absolutely nothing about "Power Test Not Run", and only talks about C wire and how to install one.  

Also, if we go to Power Info we see: 

Vin: 36.973 V

lin: 385

PS: C-385

We assume this is standard based on other blogs we read in the forum. Otherwise, the Thermostat drained the battery within a week, and currently showing 3.11v as battery power.

Can anyone help us to understand what is going on or the productis defective?

Note: we have a Nest Learning Thermostat connected on 3rd floor and that seems working fine. 

[Patrick_Caezza]

@Pkgupta 

Do you have the Nest Power Connector installed?

It sounds like you have a zoned system. Is this correct, or do you have three separate units?

If you have a zoned system, post a picture of the zone controller and how it is wired.

[Pkgupta · Accepted solution]

Had a call with Google Tech person for 45 mins and after several troubleshooting it was identified that, with 2023 models - the factory default is draw power from external C-wire connector. So, even if we have internal C-wire connected, the thermostat never detected that and looking for external C-wire connector, and as there was no connector, hence it was draining the battery. So, we disabled the options for external power connector, and now it seems drawing power from internal C-wire and battery stopped draining. Will watch and see if it holds good.

At the thermostat> settings > equipment> power connector option > power status > select Disable for external power connector, and then Restart the Thermostat.

Yes, if you don't know, it is not easy to figure out, and nowhere on Google Nest help topics - this use case is mentioned. (At least didn't find after several searches)

[Pkgupta]

@Patrick_Caezza - Missed to tag you in my response