This customer had a mild panic moment when his Apple HomeKit reported that his smart thermostat was not responding. When he checked it, the screen was blank. Luckily he still had his old thermostat and was able to connect it to get everything working again.
We replaced the failed unit with a new smart thermostat that used the same app he was already used to and the same wiring connections. There was no need to change the wall plate or adjust anything. Now he is back online and comfortable in his home.