A clogged drain hose can cause the humidifier to overflow. You can try to use compressed air to clear any obstruction, but the drain hose may have to be replaced with a new one to fully resolve the issue.
Highly Likely
02 - Float
A drum style humidifier will use a float to regulate the amount of water entering the humidifier. When the tray fills with water to a certain point, the float will rise up and shut off the water. A damaged float may not be able to shut off the water, resulting in the humidifier overflowing. Inspect the float to determine if it is obstructed or damaged and replace if necessary.
Less Common
03 - Clogged or Damaged Water Evaporator Pad
If the water evaporator pad is clogged or damaged it will need to be replaced. The water evaporator pad should be replaced at least once a year but may need replacing every 3 to 6 months depending on the water hardness. Refer to your owner's manual for guidance.
Less Common
04 - Clogged Distribution Tray
The water distribution tray is at the top of the humidifier and helps to distribute the water evenly over the evaporator pad. If the holes in the tray get clogged, water can overflow the tray. Check to see if the holes in the tray are clear or need to be cleaned. Refer to your owners manual for guidance.
