If you have an Eberle PLS unit in your home, it is a solid piece of equipment. It is not "sexy" technology, but it is efficient and dependable. If you want phone control, look into the PLS 517 Wi-Fi version. If you just want a thermostat that works and saves money, the standard PLS models are excellent.
These are common when using modern USB-to-Serial adapters. If using one, ensure it has a high-quality chipset (like FTDI) and correct COM port settings. eberle pls 514 download manual