The answer to 'why is my thermostat not working' is that there are several common causes, including a dead battery, loose wiring, faulty thermostat, or an issue with the HVAC system itself. Symptoms may include the thermostat display not turning on, the system not responding to temperature changes, or the system not turning on at all.
For simple issues like a dead battery, you may be able to troubleshoot and fix the problem yourself. However, for more complex problems with the wiring, thermostat, or HVAC system, it's best to call in a professional HVAC technician to diagnose and repair the issue. Attempting complex repairs yourself could be unsafe or lead to further damage.