If the red LED flashes very briefly, less than one second, that just means the system is changing modes within a protocol. This is nothing to worry about.
If the red LED comes on for a second or two, that means the system has detected a potential OVER TEMPERATURE condition. It may correct itself, or you may need to reduce the frequency or intensity of your protocol.
If the red LED comes on and stays on, that means a CRITICAL OVER TEMPERATURE condition has been detected. Your system is definitely running too hot and it has decided to shut down. You may see a warning screen. You should turn the power OFF. Check the coils: be sure they are plugged in all the way. A slightly pulled out coil may cause a short.
The system may automatically adjust your intensity (power level) down to a safe level, usually level 9.