If you notice that your thermostat display is blank, there are a few possible explanations. First, check to see if the power is turned on. If the display is still blank, it's possible that the batteries need to be replaced. If the batteries are fine, it's possible that the thermostat itself is malfunctioning. In this case, you'll need to call a professional for help. Finally, keep in mind that some thermostats have a "display off" setting. If this is the case, simply press the "display" button to turn the display back on.