Problem: The humidifier installed in a forced-air furnace is leaking or overflowing.
Background: A furnace-installed humidifier can overflow because it has a defective float valve, a defective float valve seat, because the unit is not mounted level or in the right position in the furnace, or for other reasons. Sometimes a humidifier may create minor overflow when the media pad needs replacement or is rubbing against the side of the unit.
What to do: First check to see that the humidifier unit is level both horizontally and vertically, using a carpenter’s level. If the unit is not level, adjust the mounting. Check the float valve and its adjustment to be sure that it is set for the right water level. (Also check to see that the float itself is not defective; if it is leaking water it must be replaced.) Inside the float valve mechanism there may be a small black rubber button that seals the valve water outlet. If the button shows wear from water erosion, reverse the but ton or replace it. Then make sure the button seats properly and evenly on the float-valve water outlet.
Special advice: In some cases a central humidifier may be installed in correctly so that its opening is located inside the “A” frame of the air-conditioner coil in the plenum of the furnace. In this case, overflowing may be the result of the high static air pressure in this location and the unit should be relocated above the “A” coil.
Helpful hint: When replacing the media pad on the media wheel of the humidifier, make sure that it does not extend past the wheel edges. Do not turn the wheel while it is attached to the motor; damage to the gears may result. Use a solution of 1 part household vinegar and 3 parts water, or a commercial mineral dissolving cleaner to dissolve lime build-up in the humidifier.