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Nest Thermostat - Taco 502, going through batteries

GEHobbit
Community Member

Just wanted to check to see if I've got this right. It's been working, but the thermostat went through the backup batteries in like a month. 

Installed new thermostat wire (ignore the green/yellow, those are extra and not connected), to run a C-wire. Wired the C wire to the COM terminal on the 24V left side of the Taco switching relay. 

Wired the thermostat. 

Operates fine, no system errors, but I get these for power readings:

Battery: "Good"

Voltage: 3.252 V

Impedance: 1422 mOhm (new batteries today)

Vin: 39.773V

lin: 385

PS: C-385

PXL_20221019_180729289.jpgPXL_20221019_180627331.jpg

10 REPLIES 10

Houptee
Silver Product Expert
Silver Product Expert

Looks normal for the voltage readings.


Houptee -- NJ Master HVAC Licensed Contractor

GEHobbit
Community Member

Any idea why it'd be siphoning batteries?

Houptee
Silver Product Expert
Silver Product Expert

Do you have zone valves in this system?

Some zone valve systems draw most of the power away and Nest causes problems with chattering valves and voltage issues.


Houptee -- NJ Master HVAC Licensed Contractor

GEHobbit
Community Member

I don't think there are any valve controls specifically?

Jeran
Community Specialist
Community Specialist

Thank you for helping out on this thread, Houptee!

Hey there GEHobbit,

Sorry about the late response on this, I'm just checking up on this thread, do you have any more questions or need any additional help?

Best regards,
Jeran

GEHobbit
Community Member

Nope! I haven't had any issues with it since replacing the batteries, so hopefully it was a fluke of some kind.

Jeran
Community Specialist
Community Specialist

Hiya GEHobbit,

Awesome, I'm glad to hear that! In that case, did you have any other questions we can address, or should I go ahead and lock the thread?

Best regards,

Jeran

Houptee
Silver Product Expert
Silver Product Expert

Do you have 2 thermostats?

I only see one blue wire to the COMMON terminal on the Taco control box.

Does the other thermostat have a C wire hooked up?


Houptee -- NJ Master HVAC Licensed Contractor

GEHobbit
Community Member

I do, but one is for the boiler and the other is for a pellet stove so has a C-wire adapter.

I think we can lock the thread.

EmersonB
Community Specialist
Community Specialist

Hi folks,

@GEHobbit thanks for getting back to us. It looks like we can consider this one complete, so I will lock the thread now. Feel free to start a new thread and we'll be happy to help.

I appreciate the help, Jeran and Houptee.

Best,
Emerson