The answer to 'why is my steam cleaner mildew' is that mildew can build up in the steam cleaner if it is not properly cleaned and maintained. Mildew can form in the water tank, hoses, and other parts of the steam cleaner, especially if the cleaner is not used regularly or stored properly. This can lead to a musty odor and potentially contaminate the steam being released.
To prevent and address mildew in a steam cleaner, it's important to empty the water tank after each use, clean the machine thoroughly according to the manufacturer's instructions, and store it in a dry, well-ventilated area. If mildew persists or the steam cleaner is not functioning properly, it's best to consult a professional cleaning technician for further diagnosis and repair.