A furnace humidifier is a piece of HVAC equipment that adds water vapor to heated air being distributed in your home. In the tutorial Anatomy of the Home Furnace Humidifier I describe the various components of the flow-through type furnace humidifier. One of those components is called solenoid valve assembly which controls water flow and is also found on most types of humidifiers.
If your humidifier is not getting water from the solenoid, assuming you have the water tap open, either the solenoid or the humidistat is bad. It’s much more common for the solenoid valve to fail over time and get stuck shut and not open, even when the humidistat is allowing voltage to the solenoid. When this happens your humidifier will stop working since it of course requires water to operate.
In this tutorial I will show you how to test to see if the solenoid has failed. Then I will provide you step-by-step instructions on how to replace the solenoid valve.
The subject of this tutorial is the General 1099 flow-though bypass humidifier as manufactured by General Filters, Inc., and the solenoid replacement process is representative of many humidifiers.