Hi Bobbyh,
Thanks for posting here in the Community forum and for showing interest in our Nest Thermostats. Are you located in North America or Europe? What is the make and model of your system? And could you send us a wiring photo of your current thermostat so I can take a closer look? You can either send the photo here in this thread or upload the photos to your Google Drive or Google Photos and send the link here so I can check.
I'll look forward to your response.
Best,
Zoe
