My diffuser will not mist. The lights are on and it is running fine otherwise. What is the problem?

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If there is water in it, it sounds like the ultrasonic unit failed.

I had the same problem. Looked up the manual online. Red light indicates water level is low I had just refilled the tank so that was not the problem but manual said to make sure water tank was firmly, securely seated on base. I unplugged the unit, unscrewed the plug on the tank and screwed it back on and then made sure the tank was securely seated on the base, plugged it in and it started working. If the tank is full you may just have to make sure the tank is fitting properly in the base.

Most misting humidifiers use an atomizer to generate the mist. It is a small metal disk that vibrates very fast. I have yet to see one of these that ever lasts more than a year or two. If you remove the water container you should be able to see the atomizer. If you can put you finger on it and it isn't vibrating then thats the problem. On most small humidifiers it is cheaper to buy a new one that to try and get it fixed.

This humidifier is AMAZING. I’m a huge fan of using essential oils (lavender, lemongrass, spruce, rose, sandalwood etc) and I picked this up from a thrift shop, added some essential oils to the water and my house smells wonderful.

Essential oil diffusers are virtually the same thing design wise except cost a fortune. This is my best diffuser! I paid $10 for it and it works so good, throws off a ton of mist which I love (it’s so dry here) and I will enjoy owning this unit for years to come. Only thing is to gently clean the little ionizer part with the brush gently and keep it clean. Also..this unit unlike newer ones does NOT shut off automatically so keep an eye on it. Running it dry might cause it to burn out.

The moisture released by this (or any ultrasonic) humidifier should not be visible, so it is very possible that it is working correctly. Try filling the reservoir and marking the water level with a small piece of tape. Then run the humidifier for a few hours, and check the water level again. If the water level is below the edge of the tape, then you know it is releasing moisture into the air, and everything is working fine.

The older style of humidifiers created a mist by spinning a disk that was partly dipped into the water reservoir. They had to be refilled often, and the mist could leave water spots or dust on nearby furniture. The water level should change very slowly in your ultrasonic humidIfier compared to a misting humidifier.

with cool mist humidifiers your not suppose to see any mist. if it's a warm mist there should be. but by your model number i'm finding that it's a cool mist. that's why your not seeing any mist.

It sounds very much like the transducer has failed. This is likely a crystal transducer and since they produce the agitation that should cause a mist, they are running continuously; not a good thing for something that is trying to shake iteslf apart all the time. These require input from a circuit that produces the fairly high level of power needed to drive the crystal so it could also be the source of the problem.
This isn't something an owner is able to diagnose unless they have some technical training.     

The Problem is minerals in the water. Impeller and ultrasonic designs send these minerals into the air. If the water in your area contains a lot of minerals, you will notice them as dust. The EPA does not issue health warnings about minerals in the air, but does recommend using low-mineral water (such as distilled water) in your humidifier. Many ultrasonic models feature a demineralization cartridge that filters minerals out of the water to prevent the dust.

Good Luck.