Nest Non-Learning Thermostat and Power Connector Issues

[EPirnik]

Hello,

My home has hydronic radiators (heat only) and all thermostats use older 2-wire cables (R and W). I have a Taco zone controller with three zones, and that has only one 24V power terminal. That terminal is currently attached to a Nest power connector and thermostat controlling my home's main zone. Works just fine.

For reference, this is the type of Nest (non-learning) thermostat I am using: Google Nest Thermostat with Wi-Fi Compatibility - Charcoal GA02081-US at Lowes.com

Recently, I added a nest to the second zone in our master bedroom/bathroom. Since I only have one 24V terminal in my Taco zone controller, I purchased a 24V / 40VA transformer to power the Google power connector feeding power to that new nest thermostat. The system is wired thusly: help wiring nest power controller and transformer to two wire - Search Images

The thermostat works fine, however I continue to see an N260 C wire error.  I updated wiring diagram in nest to show only R and W wires (I have no c-wire, thus the power connector). I am reading 28V at the thermostat plate in my bedroom. Everything looks absolutely fine. I have ensured the thermostat firmware is updated, run power tests, etc. When running the power test I get the following result:

Vin: ~28V
lin: 70 (w)
PS: W-70

Can anyone offer suggestions regarding how to get rid of this error code? Or is it simply a non-issue I should ignore, as the thermostat is in fact getting stable power? At my wit's end. Thanks!

-Ed

[EPirnik]

I should add that I DID remove the jumper inside the Nest Power Connector as per the instructions linked above. 

Thanks again.

[Patrick_Caezza · Accepted solution]

@EPirnik 

Getting the Taco valve zone controller to work properly can be a pain sometimes.

Do you know which model of controller that you have? Can you post a picture showing the complete board?

Just to verify, you followed both of the instructions on these pages, correct?

Have you tried reseting the thermostat to Factory Defaults and setting it up again?

[EPirnik]

I actually wound up throwing in the towel on the power connector. Instead, I just installed a 24V transformer in the attic and ran more wire down from up above to power the thermostat. Worked like a charm!