There is a thermistor (electronic thermostat) that detects the temperature of the exhaust and determines if the air flow is okay by the temperature it reads. If the air flow is reduced, the control displays the filter message. If it is clean, you will need to totally disassemble the dryer and clean all air flow ducts and cavities of lint, especially if the water is not making it into the condensation tray. There are a lot of parts in this machine, so you may wish to have it professionally cleaned.
Bob, January 2013
