Replacing ST9400 with Nest 3 but 240v issue

[TrevorLee]

Hi

The replacement of the St9400c looks straight forward but the thermostat is a 240v and I think the Nest expects no more than 30v so I am at a loss how to wire this myself and power the nest.  

I’m also looking to install a Nest on a second zone for heating only to replace a Honeywell but that has no power supply as it’s battery powered so just a 2 wire system. 

I thought this would be easy.

[luciaaa]

Hi, @TrevorLee!

Thank you for reaching out to the community. I'm truly sorry for the difficulties installing the Nest thermostat with a high-voltage HVAC system. I'll do my best to assist you!

Nest thermostats are designed for easy installation and are typically compatible with low-voltage HVAC systems. If you're working with a high-voltage system, your thermostat may not be compatible. However, in some cases, a high-voltage system can be made compatible with a Nest thermostat. I recommend contacting a local professional to assess your system and determine if installing a step-down transformer (to 20-30V) is a viable option.

Please remember that high-voltage thermostats should only be installed or uninstalled by a qualified professional due to safety concerns.

For more information about this, you can refer to the following article: Nest thermostat compatibility. 

Feel free to reply if you have any questions.

Best regards,

Ana