If your humidifier stops working, check the water level first. Most humidifiers have an automatic shut-off that stops them when the tank runs low or empty, so refilling it often fixes the problem. Use filtered or distilled water if your tap water is hard. If it runs but puts out little moisture, the usual cause is a clogged filter or wick, or mineral scale. Replace the filter on schedule, because a clogged one cuts output and can damage the unit.
Updated October 2026. This answer first ran in our FAQ. We've added fixes for each common symptom and the humidifier parts and care products we make.
It won't turn on, or it shuts off
Start with the water. When the tank is low or empty, the automatic shut-off on most humidifiers stops the unit, and refilling it is the fix. If the tank is full and the unit still won't run, take the tank off and set it back on firmly. On many models a float or switch under the tank has to sense that the tank is seated. Then check that the outlet works and the power switch is on. If your humidifier has a humidistat, look at the setting too. A unit set below the room's current humidity will sit there doing nothing, and that's normal.
It runs but puts out little moisture
On an evaporative humidifier, look at the wick or filter. As water evaporates it leaves minerals behind, and the wick turns stiff, crusty and discolored until air can't pull moisture through it. Rinsing won't bring it back, so replace it. A clogged filter cuts output, and it can also damage the unit, because the fan and motor end up working against it.
On an ultrasonic (cool mist) humidifier, the usual culprit is scale on the transducer, the small disc that vibrates the water into mist. Our humidifier descaler is made for that. Unplug the unit, mix 1 tablespoon into 32 oz of water, fill the base so the transducer is covered, let it soak 20 to 60 minutes depending on the buildup, then rinse thoroughly.
There's white dust on the furniture
That's mineral scale, not dust. An ultrasonic humidifier turns hard tap water into mist, and the minerals in the water come out with it and settle on nearby surfaces. Switching to distilled water stops it at the source. Descaling the transducer clears the film that has already built up.
It smells musty or sour
Standing water is the cause. Empty the tank and let it dry between fills when you can, and clean the tank and base at least once a week, following your manual. If the smell comes back right after a cleaning, the wick or filter has gone stale and needs replacing.
It leaks
Check the tank cap and its rubber seal for cracks or a loose fit, make sure the tank is seated all the way down, and set the humidifier on a flat, level surface. A base that's been overfilled by hand will also spill.
Slowing down scale between cleanings
For evaporative and warm-mist tank models, including Honeywell, Vornado, AIRCARE, Essick Air and Vicks, our humidifier tank drops go in at every refill. Use 2 drops per gallon, or about 50% more on hard water. They hold calcium and magnesium in solution so less of it ends up on the tank walls and the wick. One 2 oz bottle covers more than 550 refills. They don't replace your regular cleaning.
Humidifier parts we make
We make the Essick Air 1051 humidifier air filter for Essick Air models 4DTS 300, 4DTS 900, H12 300HB, H12 400HB, H12 600, 696400HB, 696800 and 447400HB. Note that this is the unit's air filter, not the wick (Essick Air part 1041). More in Essick Air parts and humidifier care.
Our descaler and tank drops are made in the USA. Our filters are aftermarket parts made by Think Crucial. U.S. shipping is free, and orders placed by 2pm ET ship the same business day. Need a filter or wick for a different model? Email support@thinkcrucial.com with the model number, and we'll reply within one business day.
Frequently asked questions
Why did my humidifier stop working when the tank still has water?
Take the tank off and seat it again. Many models use a float or switch under the tank, and a tank that isn't sitting fully down reads as empty. Also check the humidistat: if it's set below the room's humidity, the unit stays off on purpose.
Should I use tap water or distilled water in my humidifier?
Distilled or filtered water if your tap water is hard, especially in an ultrasonic humidifier. Hard tap water leaves scale in the unit and, in ultrasonic models, white dust around the room.
How do I know when to replace a humidifier wick or filter?
Replace it when it's stiff, crusty or discolored, when output drops even with a full tank, or when the unit smells sour right after a cleaning. Your owner's manual gives the schedule for your model.