The answer to 'why is my thermostat short cycling' is that there are several common causes, including a malfunctioning thermostat, issues with the HVAC system, or problems with airflow in your home. Short cycling occurs when the HVAC system turns on and off rapidly, which can lead to inefficient heating or cooling and higher energy bills.
Some of the most common causes of short cycling include a thermostat that is not calibrated correctly, a problem with the HVAC system's compressor or other components, or inadequate airflow due to blocked or dirty air filters. In some cases, short cycling can also be caused by oversized HVAC equipment that is not properly matched to the size of your home.