When the light on your thermostat starts blinking, it usually means that there is something wrong with the system and you will need professional help to repair or fix it. There could be something as simple as a malfunctioning sensor, stuck screen, blown fuse or noisy motor - all of which would require a technician to fix. In some cases, however, the blinking light could also mean that your thermostat is not working properly at all and you will need to replace it.