The most common type of vent fan is an exhaust fan; they tend to be used in bathrooms or kitchens to prevent the warm moist air from baths, showers, and cooking from condensing on cold surfaces, which can cause mold. Basically, the moist air is sucked in through the fan and pumped back outside the house. However, like most other electrical items in your house, they can break and below you can find some common fixes.
1 - Check the Strength
Ventilation fans come in different strengths, the larger your bathroom the higher the air-movement rating on the vent. A vent designed for a smaller room will not extract all the moist air from the room, therefore allowing mold to develop. In this case, it might be worth looking into an upgrade.
2 - Strange Noises
Generally ventilation fans are quite noisy, this is nothing to worry about, but if you notice the noise changing, then it is time to be concerned. A common reason for this could be the motor is about to burn out, a solution to this problem is to replace the motor. Ensure that the electricity is turned off before carrying out this work.
3 - Dripping
Sometimes you can find droplets of moisture on the surfaces below the fan; this is most common in the kitchen. The droplets can be sticky, oily and commonly a dirty orange colour. Simply remove the casing from the vent fan and wipe it down with a damp (not wet) cloth.