When the humidistat is calling for humidity (and the furnace is running) a solenoid valve will open and allow fresh water to flow across a porous evaporator pad. The water supply starts from a saddle valve attached to a water pipe. Water flows through a tube to a solenoid valve equipped with an inline water strainer. The valve electrically opens and closes to control the supply of water, and the strainer filters particles from the water. Filtered water then goes through the orifice which meters the water through a 1/4" feed tube (usually plastic) to the water distribution tray. From the distribution tray, water flows by gravity into the water panel evaporator (sometimes called a "filter pad") where part of the water is evaporated and enters the home's air supply ducts. Once the pad is saturated, the overflow water flushes the majority of minerals left after evaporation off the water panel pad. The water drains via a 1/2" drain tube through a drain spud at the bottom of the humidifier.
A flow-through humidifier is a relatively simple piece of equipment. The only real "moving part" is the solenoid valve, which opens to allow water flow to the humidifier. Still, flow-through humidifiers do need occasional maintenance.
Change your water panel. The typical water panel (or evaporator pad, or filter) in the humidifier is constructed of an expanded aluminum honeycombed mesh dipped in a ceramic slip (liquid clay). The large surface area of the clay material is perfect for absorbing water. When openings in the water panel become clogged with scale and mineral deposits, they will restrict airflow through the pad and should be replaced. The life of the water panel evaporator will vary with the hardness of the water, the amount of use, and the application. Is ins recommended that the water panel be changed at least once every year.
Be sure to set your humidistat at the recommend setting listed on the unit. The amount of humidity varies depending on exterior temperature.