I purchased the T9 to control my cottage heat from my home. I have baseboard electric heat with a 2 wire 24 volt relay to control the 240 volt heaters. I knew this was non-standard but was hopefully the installation manual would provide some assistance. Anyway, after about 12 hours of work, I got it working. There were several challenges to overcome. First, I needed to install another transformer to power the "C" wire and get power to the new transformer (6 hours). Next, I had to figure out how best to connect the "C" wire and "Rc" wire to complete the circuit (2 hours research). Once I got the unit powered up I thought the rest would be simple. Unfortunately, the unit would not connect to my router. I called my internet service provider and they helped me change some settings to get 5G wireless working. It wouldn't connect to 2.4 MHz because i have an extender on my router using the 2.4 MHz (3 hours). I was lucky that my ISP is a local guy willing to help (not a big company with voice mail hell). Finally, everything was powered up and connected. It took me 1 more hour to set everything up and understand the interface. Anyway, I love it now that it is working and simple to use. But, setup on a non-stanard system is not easy and Honeywell provides no assistance.
Very easy to install and has worked great. I just need to get more room sensors and then the whole house is good to go. It has definitely saved money on my hearing bill so far.
Works fine with an iPhone12. I could not get the thermostat to work remotely with my iPhone 6s. Had a persistent error message that I could not resolve