The answer to 'why is my thermostat smells bad' is that a smelly thermostat is often caused by a buildup of dust, dirt, or other debris inside the unit. This can lead to unpleasant odors, especially when the HVAC system is running. Common causes include poor ventilation, pet dander, or even mold growth.
The good news is that a smelly thermostat is usually a minor issue that can be addressed with some simple cleaning and maintenance. However, if the odor persists or you notice other issues like inconsistent temperature readings, it's best to call in a professional HVAC technician to diagnose and resolve the problem.