After finding dark residue inside a dishwasher, one homeowner went online to ask whether occasionally letting a finished load sit overnight without heat drying could cause that kind of buildup.
The replies quickly zeroed in on a dishwasher component many people forget to check: the filter.
Here's what to know
In a post shared to Reddit's r/Homeowners forum, the original poster wrote, "A few times, I've ran a load and left it overnight without the heat dry function on. Would that be enough to cause this build up over time or do you think there is mold in the water line? Either way, what's the protocol here!"
Rather than blaming the water line, many responses pointed to a more routine culprit inside the appliance. One commenter put it bluntly, "Clean the water filter ASAP."
A longer reply suggested the racks' appearance likely meant the filter had built up a lot of debris and that leaving the interior wet overnight would make matters worse. The user wrote, "That filter is probably caked if the racks are looking like that. Leaving it wet overnight with no heat dry is definitely part of the problem, it just creates a perfect little swamp in there. Pull the filter and give it a good scrub, then run a cycle empty with a cup of white vinegar on the top rack. The water line is probably fine unless you've got funky smells coming from the tap itself."
Some commenters questioned whether the residue was mold. One asked whether it could be "just the rack's enamel/coating coming off," and said a similar-looking problem in their own dishwasher turned out to be corrosion.
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More background
Heat also came up repeatedly in the thread. One wrote, "the dishwasher should be hot enough to kill mold, it must not be working here," while others said a broken heating element had caused similar recurring buildup in their own machines.
Unresolved dishwasher problems can become expensive. A clogged filter can reduce cleaning performance and leave debris behind, while a faulty heating element can lead people to rewash dishes, waste water and electricity, or even replace the appliance sooner than necessary.
Regularly inspect and clean your dishwasher's filter. In many units, it sits at the bottom beneath the lower rack and can be removed by twisting it out. If it is coated with trapped food or slime, a thorough scrub may solve the problem before it gets worse.
Another helpful check involves the machine's heat. Commenters suggested pausing a cycle to see whether the water is hot, though owners should always do so carefully and follow manufacturer guidance. If the heating seems off, the issue may require a repair rather than more aggressive cleaning.
Where can I learn more?
• Many households can save energy by cleaning the dishwasher filter they rarely notice.
• An appliance maintenance expert says dishwasher maintenance mistakes can make machines fail sooner than expected.
• A dishwasher scientist warns common loading habits can waste money, water, and cleaning power.
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