A method for controlling a humidifier of a CPAP device including a controller, the method including controlling a heating element in the humidifier with command signals from the controller, sensing a temperature of a fluid in the humidifier with a sensor in the humidifier that transmits signals to the controller, establishing an acceptable operating range for the signal transmitted to the controller, determining whether the transmitted signal is within the acceptable operating range, if the signal is within the acceptable operating range treating the signal as being indicative of the temperature of the fluid in the humidifier and using the signal to control the heating element, and if the signal is outside of the acceptable operating range, the controller determines the humidifier to be unavailable.