Customer informed me there was an error code on thermostat reading ERROR 53. Error code 53 is displayed when the thermostat detects an issue with the outdoor temperature sensor. Outdoor temperature sensor was fine and was not an issue. Attempted to reset thermostat to get rid of code. Thermostat continued to display error code.Informed customer that thermostat will need to be replaced under warranty. Returned later in the afternoon to install new upgraded thermostat. After installing new thermostat, tested operation of features and heat mode. Will have to return for AC tune up another day. Was unable to attach hose to the spigot near AC unit. AC unit was making loud rattling noise. I added a screw on access panel and tightened. AC unit sounds much better.