Nest Thermostat error 261 using the power adaptor

[DrPing]

I installed a nest thermostat using the nest power adaptor, I only had two wires going to my stat. The system works just fine, should I be concerned with the error 261 code. I know this code is related to  the missing C wire, that's why I used the adaptor. It's wired to a Taco zone valve panel. Like I said it works fine.

[Patrick_Caezza]

@DrPing 

Yes, you should be worried and you will have battery problems at some point.

Taco zone valve controllers can be a major pain depending on which model you have.

You usually will need an external 24vac transformer when using the Nest Power Connector with a Taco valve controller.

This is the recommended wiring when using one.

[DrPing]

Are you saying I should add a 24V transformer and not connect the C wire to the transformer in the Taco panel? 

[AxelD]

Hi DrPing,

Thanks for posting in the Community! I'm sorry to hear you encountered the N261 error, but it's great that your Nest Thermostat is working correctly now. As you mentioned, this error typically indicates that the C-wire isn't receiving enough power.
 

To resolve this error, you can either install a C-wire or use a Nest Power Connector. If you already have a Nest Power Connector, consider contacting a local HVAC technician or Nest Pro for a professional checkup.
 

Thanks to @Patrick_Caezza  for providing the correct installation diagram.

Here are some resources to help you troubleshoot C-wire issues:

Troubleshoot Nest thermostat help codes
Learn about the common or C wire

Please let me know if you have any other questions.

Regards,
Axel.

[Patrick_Caezza]

@DrPing 

Can you post a picture of the Taco valve controller?

Those controllers normally don't have enough power for a smart thermostat. Depending on the model # you might be able to add a second transformer.