The answer to 'thermostat not working' is that there are several common causes, including a dead battery, wiring issues, a malfunctioning thermostat, or problems with the HVAC system itself. Symptoms may include the thermostat display not turning on, the system not responding to temperature changes, or the HVAC system not turning on or off as expected.
For simple issues like a dead battery, you may be able to replace it yourself. However, for more complex problems with wiring, the thermostat, or the HVAC system, it's best to call a professional HVAC technician. They can diagnose the issue, make any necessary repairs, and ensure your system is working properly and efficiently.