The Aprilaire 4004 In-Line Strainer is a tiny strainer that fits in the inlet fitting of the water solenoid valve which allows water to enter your humidifier. It is designed to keep debris from entering the solenoid valve and should be checked periodically. See the owner's manual section labeled "Periodic Preventative Maintenance" for more information. Used in all models except for Commercial units and residential models 110, 112, 445, 445A, 448, and 330.
Get it straight from the source! Genuine Aprilaire replacement parts made by Aprilaire in Poynette Wisconsin U.S.A.
If the valve is caked with hard water deposit you might as well forget about getting it out. I had to purchase a new valve. Unfortunately you have to buy the solenoid with the valve which runs the price up.
4004 In Line strainer
It is very hard to remove.
Remove used 4004
Easy method to remove: Easily turn in a small wood type screw (by hand with just a soft bite of engagement)and then pull to rremove.