The answer to 'why is my pressure washer moldy' is that mold can build up in the water lines and storage tank of a pressure washer due to stagnant water and lack of proper cleaning and maintenance. Mold can cause the pressure washer to malfunction and can be a health hazard if inhaled.
To prevent mold, it's important to empty the water from the pressure washer after each use and store it in a dry, well-ventilated area. You should also clean the pressure washer regularly by running a vinegar or bleach solution through the system to kill any mold or bacteria. If the mold is severe or you're unable to fully clean the pressure washer, it's best to call a professional cleaning service to inspect and service the equipment.