| Problem | Possible Cause | Solution | | :--- | :--- | :--- | | | Power is off, or wiring is incorrect. | Check the circuit breaker. Ensure the thermostat's on/off switch is on (if it has one). Verify the 24VAC power connections. | | System Won't Turn On | Loose wiring, incorrect mode setting, or a system protection delay. | Check all wire connections. Make sure the thermostat is set to "Cool" or "Heat". Wait 3-5 minutes for the built-in compressor time delay to finish. | | Display Shows "Er" | Temperature sensor failure (internal or external). | This indicates a sensor error. You will likely need to call a technician to replace the faulty sensor. | | Temperature is Wrong | Poor thermostat location or an incorrect temperature offset. | Check if the thermostat is near a heat source, draft, or in direct sun. If not, adjust the Temperature Offset in the installer settings. | | Buttons Don't Respond | The thermostat might be locked or in an error state. | Try turning the unit off and on. If it's a touch model, ensure the surface is clean. If not, cycle the power to the unit at the breaker. |