The humidifier detects when the water fails to drain (or the level is too high), by checking the level sensor status after opening the drain solenoid valve. If sensor activation is not detected within the time set by parameter “Tmax drain”, the humidifier keeps the drain solenoid valve open and activates the wait procedure, as described in the previous paragraph, displaying alarm Ed. The humidifier will reset the alarm andresume normal operation when the low water level is correctly measured.