We had an Aprilaire humidifier (600 model) installed in a new house 2.9 years ago. About a year ago, the humidifier began leaking water all over the basement floor. This has happened 3 times with 3 visits from a heating a cooling company tech to fix the problem. We just had the biggest flood yesterday - water was literally pouring out of the I think the front of the humidifier. I need to know what to ask the h/c technician who will come again to fix the problem. Doesn't it seem that there is broken part that should be replaced to stop this from happening? I know nothing about humidifiers and neither does my husband and we're about ready to toss it out. Any tips would be appreciated.

  • The big question is why is it leaking. A broken valve? Solenoid stuck open? Seam coming apart? Could be all kinds of things. Pictures might help - someone familiar with the unit might spot a problem. Mar 31 '19 at 18:03
  • So you have 100% humidity now. If the unit keeps malfunctioning then it may be wise to replace it.
    – Alaska Man
    Mar 31 '19 at 20:03
  • I assume you're changing the filter each season? Until the issue is solved, I'd leave the humidifier off. Apr 1 '19 at 13:33

Here is a diagram of that model from Aprilaire. The drain tube (#9 in the diagram) might be clogged. Look on page 11 section 9 for further instructions about the drain tube. Also, check the main water outlet where the tube connects to the bottom of the pan to make sure drainage isn't restricted. Check the pipe that the drain tube is connected to. It could be clogged as well.

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Humidifier is a simple device, you need a new heating guy. 3 visits and he can't solve it. Not good. A handy friend should be able to identify the problem in a matter of minutes. Clogged drain, misaligned pad, cracked or dislodged 1/4 " water supply. Even if the solenoid was stuck open it should not leak.


The problem I have seen is a small chunk of scale or sand blocking the valve from closing. I started installing mesh screens prior to these valves similar to what is used in washing machines. The screens do need to be cleaned when they plug up with scale and debris, but this is better than a flood. Depending on your supply line, a small inline filter may be a good choice, but this has been the cause for several leaks that I have found. With both the mostly plastic valves and the more expensive brass and stainless models, I have disassembled the valves and been able to clean them. When the valve gets ~8-10 years old the diaphragm needs to be replaced. On the brass ones there are rebuild kits for ~$15. The plastic ones I just replace.


The Aprilaire humidifiers, including the 600, use an orifice piece to restrict water flow. It should be at the end of the line coming into the solenoid, but someone may have put it on the other end. It will be yellow or red, you need yellow for your model.

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I had the same problem with lots of water leaking from the bottom almost as soon as the unit turns on. If that is your problem too (leaking within a second or two after being turned on) then maybe the water is coming out of the inlet too fast -not at its normal slow trickle- in which case the jet of water is splashing out of the tray and onto the fan housing. That is what I observed with mine.

One easy way to tell if too much water is coming in- First crack open the humidifier housing so that it turns off while the HVAC fan is on. Then briefly close the humidifier housing so the humidifier turns on for 3-4 seconds (its fan should spin and water should flow). Then open the humidifier and look at the panel. If you see water cascading along the outside face of the water panel and mainly down the center 1/3 of the panel, then somehow too much water is coming out of your inlet.

Alternatively, a sure fire way to see is to disconnect the electrical connector on the housing - just pinch the plastic sides of the connector to remove it from the housing. There should be enough slack in the wire to allow you to make the connection without closing the housing. Obviously be careful because the fan will spin and make sure you keep the correct orientation of the connector when connecting. Once you make the connection the fan will spin and the water will flow and you'll be able to instantly tell whether or not too much water is coming in from the inlet.

For me the water was jetting in so fast it was ricocheting off the upper tray and onto the fan housing. As a temporary fix I dialed down the saddle valve so it wasn't open all the way.

But is too much water from the inlet (~3 times as much as normal) the fault of the solenoid? I just replaced the solenoid a few months ago from having the opposite problem of no water flow.


I replaced the yellow orifice at the solenoid outlet and it fixed the problem. I verified the water was coming out to fast/strong from the original orifice. The outlet hole in the original orifice must have somehow enlarged. Hard to believe this happened.

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