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Several "continuous" dehumidifiers all had the same problem. There is a bucket to collect water, and also an outlet for a hose where the water can flow out so water does not collect in the bucket. With a hose connected, from time to time, the bucket does fill up with water and then the float switch stops the machine.

I had this problem with 5 machines from 3 manufacturers over the last 15 years. With each one:

  • The hose is not blocked. Water does flow from the unit into the drain. After I empty the bucket water continues to flow. The bucket does not immediately start to fill up again .... but sooner or later, weeks or months, it does.
  • I place the dehumidifier up on blocks and the end of the hose inside a sump pit, so there is about 3 feet of vertical fall through the hose. The hose is not very long. About 6 feet. It does not coil or rise back up at any point.

My point is, there is no blockage. There is something that causes water to enter the bucket and fill it up under certain circumstances.

There must be something about the design of all these that is causing this.. Any clues?

(I've had Frigidaire, Delonghi, Kenmore).

[Edit] Adding some pics and thoughts on answers and comments

I disassembled several of the units, and they all used the same simple system to select hose or bucket: There is drip tray to collect moisture and the tray has two outlets, one higher than the other. The lower outlet goes to the hose. If it is sealed with a cap it fills up, and the water rises to the level of the higher outlet that goes to the bucket. It's impossible to photograph this without destroying the machine so here is a diagram: enter image description here

Answers to questions in comments:

  • Is there a valve that might be failing? No
  • Is the hose big enough? Yes, it’s a regular garden hose. The flow varies but at its greatest it’s a fast drip.
  • Ice because of dirty filter? No. I clean my filters regularly and at the most recent occurrence it was clean.
  • Ice because of low temp environment ? No. It’s a basement in the summer. About 70 degrees and 55% RH all the time (except after the bucket becomes full).
  • Ice, we don't know why? This one is intriguing me. It’s the only viable explanation so far. The only way for the water to rise to the bucket outlet is for the hose outlet to be blocked. The only way for the hose outlet to sometimes randomly be blocked, but never when I’m looking, is ice. I have to think about this one.
  • Hose not tight enough? That’s not the problem. In my current unit, and at least one other one, the hose outlet is outside the cabinet. If it were loose the water would drip on the floor. enter image description here enter image description here

[Edit 2] Leading theories

Some truly enlightening discussion in the answers and comments here. I'm going to summarize the leading theories that I intend to test through experimentation in the coming weeks:

  1. Negative Pressure at the continuous flow exit hole produces an inflow of air that prevents water from dripping out. Water collects in the pan. It drains out between cycles or, if there is enough humidity, it backs up to the point that it drains out to the bucket. The bucket exit hole is vertical, and it is usually larger than the continuous hole so it does not suffer the same problem.
  2. The negative pressure theory would be exacerbated by a dirty filter, and by periods of high humidity such as after a storm, and by setting the machine's fan to run continuously rather than in cycle with the dehumidification.
  3. Gunk buildup in the hose limits outflow, normally not significantly but during periods of peak humidity the limitation is enough to cause water to back up and overflow the pan into the bucket.
  4. Possibly the two above things combine. Possibly gunk buildup near the continuous exit hole increases air inflow velocity to exacerbate the problem.
  5. Possibly a P trap in the exit hose will help.
  6. Possibly flushing the exit hose periodically will help. Maybe manually annually, or maybe by connecting the hose to the bucket instead of the hose connection, as described in one of the answers.

[Edit 3] An update, one month later

Edit 3 is 33 days after Edit 2. I've been watching the bucket level indicator daily. We have had a couple of rain storms over the past month where there was more moisture in the basement walls and air than usual. The bucket remained empty throughout. Not a drop of water in the bucket, ever ... until today. Between yesterday and today, the bucket filled up and the machine stopped. It was a bone dry day. It rained lightly yesterday, nothing special. Temps are in the 70s. I checked the hose, and ran water through it from a garden faucet ... it's completely clear and unobstructed.

I can positively say that high humidity, ice, and gunk are not the cause. of the bucket filling up today.

The only remaining theory is negative pressure. This is corroborated by my internet tutorials on a similar problem with central A/Cs.

I have created a makeshift "trap" for my unit using its cord keeper. It will be hard to say conclusively if this is working or not, since I cannot correlate this with weather or anything else, and it's quite normal to go more than a month without the problem. But we'll see.

enter image description here

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Michael Karas
    Sep 9, 2021 at 5:18
  • I have ruled out ice, gunk, and wet weather as being causes of the bucket filling up. The only remaining theory is negative pressure, and while the randomness of it remains unexplained, I've added a trap as explained in an update to the question. TBD.
    – jay613
    Oct 12, 2021 at 0:36

6 Answers 6

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I want to give Glen Yates the credit for cracking this (at least for my situation, which may or may not be the same as the OPs) but his comment on the question about p-trap put this together for me. My basement is pretty damp without dehumidification. Better drainage has helped but if I don't run a dehumidifier 3-seasons of the year, my tools rust, and anything that absorbs humidity like paper or cardboard will be damp to the touch. I've dealt with a number of issues like the tilt of the dehumidifier, pinched hose, clogged hose, etc. and it works reliably now, with one particular exception: when we get heavy rains, I have learned that I need to go down and check the bucket. It will often be filled and the dehumidifier stopped.

This didn't make sense to me. How could it be that the dehumidifier was pulling more water out of the air than a garden hose can handle? But then Glen mentioned a p-trap. And I looked into it and it all makes sense. The p-trap on a AC unit is there to prevent air from coming into the unit through the condensate drain as described here:

Since the Air Conditioner is at a negative pressure relative to the outside air, the outside air will rush into the air conditioner through any openings (the condensation drain, is an opening). On our A/C the air rushing in through the condensation drain was preventing the water from exiting through the drain.

Now it makes sense why I'm seeing that. A dehumidifier is very similar to an AC unit. If it's pulling air through the drain line, water can't exit through it and it ends up in the bucket. In normal circumstances, the unit will cycle frequently enough that the water doesn't reach the level required to go into the bucket (per your drawing.) But if it's running continuously for a long time, there's no pause in the negative pressure and it will drain to the bucket and then stop running once it's full.

So I'm going to be hooking up a p-trap on the drain connection of my unit. Maybe this will help you as well. I found this page which has a lot of technical details around p-traps and includes this helpful image:

enter image description here

Initially I wrote that I thought the image is inaccurate because water will find it's level. But if it's under negative pressure, perhaps the image shows the amount of water column height needed to keep it from being pulled into the pan. I just had this happen again and it was after a heavy rainfall that lasted for multiple days.

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    "If the negative pressure were enough to suck water back up the pipe, it would also suck the water off the evaporator and blow it back into the house." Sorry busy morning and I just looked more closely at this. I don't think the negative pressure is enough to suck water up the hose/pipe. A p-trap wouldn't help if that were the case. It's air that's being pulled in. Water is 400x heavier than air. That airflow back into the pan prevents water from going into it. Keep in mind, there's no water column in the pan to hold back the air which is what the p-trap creates.
    – JimmyJames
    Sep 8, 2021 at 14:53
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    @jay613 "why does the negative pressure (if that is the reason at all) SOMETIMES prevent water exiting but not always?" That's actually what clicked on the lightbulb for me. Most of the time, my dehumidifier runs for a while, then stops, runs again, stops, etc. When that's happening, there are no issues. It's only when it's running nonstop all day that I get water in the bucket. So the hypotheses is that when it's running, it's collecting in the drip pan, and shuts down before it goes above the 2cm or so that causes it to drop into the bucket.
    – JimmyJames
    Sep 8, 2021 at 15:01
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    "The exit hole to the bucket should suffer exactly the same fate. If the fan is on constantly (as I believe it is)" I think it's the fan that causes the negative pressure so if your fan is running constantly, that would suggest this is not a viable theory. Mine does not run constantly. One thing that is different is that the hole to the bucket is positioned vertically and the hole to the drain is horizontal. Imagine blowing air in each and which would be easier to stop water flowing from. Also, it might not be all or nothing. Maybe the drain is just slowed enough to back up.
    – JimmyJames
    Sep 8, 2021 at 15:07
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    I added a makeshift trap by simply looping the hose as shown in my last question edit. The problem has not recurred in a year. Test successful. Answer marked correct.
    – jay613
    Sep 3, 2022 at 12:19
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    @jay613 I was thinking that it would need to be filled but I realize now that as long as you don't have the continuous run issue right off the bat while it's dry, it should fill on it's own.
    – JimmyJames
    Sep 6, 2022 at 18:01
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This sounds like a leak at the internal connection from the bucket drip point to the hose adapter.

Internally, our Artic King dehumidifier has a small pipe coming out of the dehumidifier over the bucket. It also has an attachment to convert the unit from bucket to hose. The attachment consists of a plastic flange for the hose to attach to and a short piece of flexible plastic hose that press-fits over the bucket drip pipe. The plastic hose is only press-fit and I see how it could stiffen over time, no longer press firmly over the bucket pipe, and start leaking into the bucket.

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  • 4
    Yup, that's what it is. Hose leak right at the coupler, or faulty gasket in the coupler, or in my case a limp wrist doing the tightening. Sep 5, 2021 at 21:33
  • The problem with my current unit and at least one previous one is not a loose hose or gasket. I can't be sure about every one of the units that did this, but in my current and previous one the hose outlet is outside the cabinet. A loose or faulty fitting would cause water to drip on the floor, not in the bucket. Will add photo to question.
    – jay613
    Sep 6, 2021 at 11:31
  • To further clarify, one of my previous units had a "hose adapter" that INTERNALLY screwed into the machine but my current and all other ones had a hose "outlet", fully and permanently integrated into the inner drip tray and sticking outside the machine where the hose attaches.
    – jay613
    Sep 6, 2021 at 11:58
  • The design in your pictures is different from my unit, so it appears that a loose internal hose may not be the problem, at least on the present unit. Sep 6, 2021 at 14:12
7

Here's one further possibility: an ice blockage.

If the airflow is too weak (dirty filters, externally obstructed, or a failing fan), or the humidity very high at fairly low temperature, ice builds up on the coils. Then the heat pump cuts out, but the fan might keep running. The ice should melt and drip, but it can come off in lumps, and those can block the hose outlet. They'll melt by the time you can strip the machine down. I've had the same effect cause an intermittent leak onto the floor because the outlet from the drip tray to the bucket blocked.

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  • Ice. Hmmm. Random occurrence, never when I'm looking, comes and goes. This is a good lead. It's not as simple as "high humidity at low temp" because this is a basement, in the summer, with a dehumidifier so the temperature and humidity is fairly constant. But maybe something is causing the hose exit hole to ice up.
    – jay613
    Sep 6, 2021 at 11:36
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    I too had exactly this happening to me. The basement was about 20 °C (68 °F) but humidity was high, being near the seaside - 60% to 80% all the time. Luckily, my drip tray was 5 cm deep, so I could just stopper the drip tray outlet without risking flooding the floor.
    – LSerni
    Sep 6, 2021 at 13:43
  • @LSerni could you determine what was causing the water to a) stop flowing through the hose and then later b) start again? Otherwise, if you plug the drip tray drain, and the hose has this problem, the water will eventually go on the floor. Can you explain any more?
    – jay613
    Sep 6, 2021 at 15:51
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    @jay613 in my case, I saw a large ice shard floating in the tray, being sucked against the hose outlet and sticking there. I had a DeLonghi with "de-icing" system, it heated the cold coil somehow so that instead of slowly melting, the ice would just fall down in solid form. Who knows, maybe protecting the area with some large-mesh steel net would have worked too. By stoppering the other outlet, the water accumulated in the tray and the ice had time to melt down, or maybe it was just floated upwards, unblocking the hose. But you're right, a shallow tray would have flood the floor.
    – LSerni
    Sep 6, 2021 at 16:19
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If the dehumidifier uses a pump to actively remove water from the collection bucket, then it could be an issue with the controls system. We had a cheap dehumidifier that had to be set explicitly to "continuous mode" before it would employ the pump. Unfortunately if the device lost power at any time, it would forget and reset itself to the default "bucket mode" when it booted back up.

The solution was to return it and buy a more expensive brand that the manufacturer confirmed would remember its settings between power cycles.

This problem seems less likely if your system relies on gravity to drain, but it's still possible that there is some electronically controlled valve that's getting shut off.

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    good old market segmentation right there. Buy a more expensive one for something it should be able to do anyway.
    – user253751
    Sep 6, 2021 at 8:13
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    My cheap one just uses fluid flow to select continuous or bucket. If the water can get out the hose hole, it will. Simple and foolproof, unless the fool loses the screw cap for the hose fitting
    – Chris H
    Sep 6, 2021 at 8:45
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    One of my dehumidifiers had a pump option that I never used. None of the others even had a pump. The problem I am describing is with units that employ gravity. As @ChrisH describes, and I'll add a diagram to the question soon ... if the water can fall out the hose it does, but if it's capped off the water backs up and falls out another hole into the bucket.
    – jay613
    Sep 6, 2021 at 11:34
3

Having had this many times on various dehs over the years it seemed to be a consequence of the drain hose becoming blocked with some sort of slime that presumably grew in the presence of moisture and dust in the circulated air that would contaminate the condensate

The slow flow experienced by a relatively narrow hose seemed to further exacerbate the problem as did the small amount of water emitted regularly in continuous drain mode. In the end I made a modification to the bucket that resolved things and have since run a deh for several years without tending to it at all:

enter image description here

I drilled a hole in the side of the bucket (blue), below the maximum water level (yellow) defined by the float mechanism that shuts off the deh, and slightly smaller than the hose (red) outer diameter, so that the hose made a good seal when pushed through the hole. The end of the hose was cut at an angle to prevent it sucking flat against the base of the bucket. The deh was placed higher than the end of the hose outlet (only about 6 inches; deh on a worktop next to a sink).

The deh would dump into its bucket continuously, eventually filling the bucket to a level where a siphon started down the hose, at which point the hose would rapidly empty the bucket. The higher velocity of the water seems to keep the inside of the hose clear of slime and also cope with any slime in the bucket; far from the hose there appears to be some buildup on the bucket floor but near where the hose picks up it's relatively clean..

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  • I like this idea. Although, if the explanations here are correct it might be better to just flush or replace the hose a couple of times a year. The fact you've had it running reliably for years is great.
    – jay613
    Sep 7, 2021 at 21:44
  • Looking at the discussion in another answer about using a P-trap, I wonder if the problem you solved here was not "flushing the pipe" but rather, avoiding the negative pressure problem? And if it would be sufficient to install a P trap on the usual continuous flow connection and flush the hose manually once a year or so. I'm going to experiment.
    – jay613
    Sep 8, 2021 at 15:19
0

I've seen gelatinous blobs of some kind of fungus living in a dehumidifier. You might have one of these blobs occasionally getting big enough to block the channel that leads to the the drain hose, backing up the condensate until it spills into the tank.

Unscrew the hose and have a look into the nipple with a flashlight to see if something is growing in there. If you can see the drainage channel from another angle, that would be helpful. If something is growing in there, it's time for a cleanout. Follow your dehumidifier manufacturer's instructions for cleaning and sanitizing the unit.

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  • I've seen that gunk too in my older machines, but I determined that they were NOT blocking the exit or the hose. I tested for that. Also, my current machine is less than two months old and has absolutely no mold, fungus, dust or anything else collecting or blocking anything. I've already had the problem twice. But note, the hose DOES WORK. If it were not working, the bucket would fill up several times a week.
    – jay613
    Sep 6, 2021 at 15:53

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