A diagnostic method for a clothes treating apparatus comprising a heat pump having a compressor, a condenser, an expansion apparatus, and an evaporator, the method comprising the following diagnostic steps: activating the compressor; measuring a temperature T1 of the refrigerant that has passed through the compressor; re-measuring a temperature T2 of the refrigerant that has passed through the compressor after a predetermined period of time has passed; checking whether or not a value F that is definied as T2 - T1 is greater than a predetermined value; characterized by; if the value F is greater than the predetermined value: checking whether or not the execution number of the processes each comprising the afore-mentioned steps is greater than a predetermined number; - if the execution number of the processes is not greater than the predetermined number: suspending the operation of the compressor and repeating the foregoing processes; and if the execution number of the processes is greater than the predetermined number: - determining that a failure has occurred in the clothes treating, and - notifying the user that the time of cleaning a lint filter has arrived when determined that a failure has occurred in the clothes treating apparatus; the method further comprising: sensing whether or not the lint filter is detached and attached thereto subsequent to notifying that the time of cleaning a lint filter has arrived; performing the above diagnostic steps when sensed that the lint filter has been detached and attached thereto; and notifying that the time of cleaning an evaporator has been arrived when a failure has occurred in the clothes treating apparatus. activating the compressor; measuring a temperature T1 of the refrigerant that has passed through the compressor; re-measuring a temperature T2 of the refrigerant that has passed through the compressor after a predetermined period of time has passed; checking whether or not a value F that is definied as T2 - T1 is greater than a predetermined value; characterized by; if the value F is greater than the predetermined value: checking whether or not the execution number of the processes each comprising the afore-mentioned steps is greater than a predetermined number; - if the execution number of the processes is not greater than the predetermined number: suspending the operation of the compressor and repeating the foregoing processes; - if the execution number of the processes is not greater than the predetermined number: suspending the operation of the compressor and repeating the foregoing processes; and if the execution number of the processes is greater than the predetermined number: - determining that a failure has occurred in the clothes treating, and - notifying the user that the time of cleaning a lint filter has arrived when determined that a failure has occurred in the clothes treating apparatus; - determining that a failure has occurred in the clothes treating, and - notifying the user that the time of cleaning a lint filter has arrived when determined that a failure has occurred in the clothes treating apparatus; the method further comprising: sensing whether or not the lint filter is detached and attached thereto subsequent to notifying that the time of cleaning a lint filter has arrived; performing the above diagnostic steps when sensed that the lint filter has been detached and attached thereto; and notifying that the time of cleaning an evaporator has been arrived when a failure has occurred in the clothes treating apparatus. sensing whether or not the lint filter is detached and attached thereto subsequent to notifying that the time of cleaning a lint filter has arrived; performing the above diagnostic steps when sensed that the lint filter has been detached and attached thereto; and notifying that the time of cleaning an evaporator has been arrived when a failure has occurred in the clothes treating apparatus.