Product review (5 stars): It looked like the humidifier had never been serviced
Purchased a twin home that had an Aprilaire humidifier attached to the furnace.  It looked like the humidifier had never been serviced.  The screen In the unit was covered with a lot of white calcium.  I purchased the Aprilaire Maintenance Kit.  It had all the parts that I needed to replace the parts in the Aprilaire humidifier.  I followed the instructions that came with the kit which made the servicing easy.  When it is time to service the unit again, I will order another maintenance kit.