Hey everyone, I wanted to share my experience with integrating multiple Honeywell RTH9585 Smart Thermostats into my SmartThings setup. At first, I was a bit puzzled because I could only get one thermostat to connect through the linked TCC. When I tried adding the second and third ones, I kept getting the message that they were already installed. I was a bit stuck, but after some research and trial and error, I figured it out!
Here’s what worked for me:
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Check the TCC Connection: Ensure that your TCC (Thermostat Control Center) is properly linked to SmartThings. This was the first step, and it was crucial.
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Use the SmartThings App: Instead of trying to add them through the Honeywell app, I used the SmartThings app to discover new devices. It worked like a charm!
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Give It Time: Sometimes, devices take a bit of time to fully integrate. I gave it about 10 minutes, and voilà, all three thermostats showed up in my SmartThings ecosystem.
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Check for Updates: Make sure your SmartThings app is up to date. I did a quick update, and it made the process smoother.
I was so relieved when everything connected properly! Now, I can control all three thermostats from one place, which is super convenient. If you’re having the same issue, I hope this helps! 
Any other tips or experiences with multiple Honeywell thermostats? I’d love to hear them!