Tom Lohr is an avid home improvement enthusiast. He prefers to spend the money he saves on new tools and gardening supplies.
Keep it Moist
Electromechanical devices can be finicky, especially when they control the flow of water. The solenoid on your whole house humidifier is no different. It's considered a high failure part of your HVAC system. If you have been troubleshooting why your furnace humidifier is running continuously, there is a good chance you will also find that the solenoid is not performing as advertised.
The water flow solenoid on your whole house humidifier is a simple device. It's a small, electrically activated valve that turns the flow of water on and off. A 24 VDC signal from the humidistat tells it when to open and close. If everything on your humidifier seems to be working, but there is no water flow, it is usually one of two things: the supply valve is turned off, or the solenoid had stopped working. You may also hear a weird mechanical moaning noise when the water to the humidifier is activated; that is a clear signal that your need to replace the solenoid.
While no HVAC failure is pleasant, the good news is that replacing the solenoid is easy and relatively inexpensive. Most units use the same type of solenoid, and you can easily find one on Amazon for around $30. A visit from an HVAC repair person will set you back well over $100.
If you need to replace the solenoid on your unit, follow these simple steps:
1. Turn Off the Humidistat
The humidistat sends a 24 VDC signal to activate the solenoid. While not dangerous, you don't want it trying to turn on the solenoid while you are in the middle of replacing it. Simply turn the knob on the humidistat to “off.”
2. Shut Off the Water Supply
Hopefully, the water supply line to the humidifier has its own shutoff valve. If not, you might want to consider installing one. Wherever your water supply shutoff valve is to your humidifier, close it.
3. Drain the Water Out of the Supply Line
Get a small bucket or cup (there is not much water in the supply line, but enough to make you wish you had captured it before it made a mess). Using a wrench, unscrew the water supply line and quickly put the end of it in the bucket.
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4. Remove the Other Water Line
Having removed the water supply line, now remove the same type of line on the other side of the solenoid. There may be a small amount of water in this line as well so have your bucket ready.
5. Remove the Electrical Wires
There are two wires that run to the solenoid. Remove them. Usually, the two permanently attached wires to the solenoid join the wires from the humidistat near the solenoid. Normally, a wire nut connects the two.
6. Unbolt the Solenoid
While the location of your solenoid may be different, the bulk of them are bolted onto the furnace or ductwork near the humidifier.
7. Install the New Solenoid
Bolt the new solenoid to the same location as the old one. Reconnect the water and electrical lines. It is basically the reverse of removing the faulty solenoid. NOTE: the solenoid is designed for water to flow in one direction. There is an arrow somewhere on the solenoid that indicates which direction to install it.
8. Check for Leaks
It is best if you are standing by with a bucket and someone else turns on the water supply valve. If not, you can do it yourself, just be quick about getting the bucket underneath the solenoid if it is leaking.
9. Test Your Work
Now that the new solenoid is installed, check to ensure that it works. Turn the humidistat to its highest setting. After it turns on, you should be able to hear the solenoid open and the water flowing. Check for leaks again, and if there are no leaks, put your tools away. You are done.
Don't Let Your HVAC System Drain Your Wallet
HVAC companies make a killing on fixing small issues on furnaces that you can do yourself. The bill for replacing the solenoid on your humidifier won't be pretty, so save the cash and do it yourself. The tools required are common and minimal, and even the novice DIYer can complete a solenoid replacement.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.