Getting rid of mold in a dishwasher

March 28, 2017 11:24 AM

How would you get rid of persistent mold in a dishwasher?

We have a 12 year old Bosch dishwasher. In the last couple of months, grey/dark mold has started to build up in the dishwasher. Not on the dishes themselves, which seem perfectly clean, but on the inside surfaces of the dishwasher. The dishwasher otherwise works well, although it does seem to take longer to complete a cycle than when it was new. We use Kirkland liquid detergent and Finish rinsing agent with every cycle.

While the dishes look clean, it does not seem healthy and we are seriously considering getting a new dishwasher because of this but I want to give it one last shot.

I have seen this previous question but we have tried most of what was suggested and it keeps coming back.

So far, we have tried:
- Disassembling and scrubbing all part we can reach and with soap and water
- Run complete cycle with Vinegar
- Run complete cycle with Lemon juice
- Run complete cycle with commercial Finish/Sunlight dishwasher cleaner

I have not tried bleach as it is supposedly very bad for the stainless steel interior.

I will be ordering some Steramine Quaternary Sanitizing Tablets that are suggested in the previous question, to see if it will make a difference.

Have you had to deal with a similar situation and if so, how did you get rid of the mold monster once and for all?

posted by TinTitan to Home & Garden (9 answers total)

What inside parts of the dishwasher ? The tub itself, or the racks, the spray/nozzle, the door ?

Our dishwasher gets mold on the door, but it's the part of the door that is outside the rubber-gasket/seal (ie so it isn't hit with water when running). It gets damp (drips when loading, steam when running etc), but not washed by running the cycle. So I sponge it off with my lysol bucket when cleaning the kitchen.
posted by k5.user at 11:35 AM on March 28, 2017

Best answer: This happened in my old dishwasher when the heating element broke. I tried cleaning it with one of those dishwasher cleaners with a wax plug that melts in the heat, and it never melted, so it clued me in.

Fixed the heating element and it never came back. A dishwasher should get hot enough to kill any developing mold every time it runs.
posted by sanka at 11:41 AM on March 28, 2017

Response by poster: k5.user: Mostly the top and bottom of the tub, with some on the sprayer and on the door where it is touching the racks. There is also some around the door gasket that we clean as you do.

sanka: That is an interesting take. The wax plug on the cleaner did melt but maybe my element is just inefficient and not completely broken. Could also explain why the dishwasher is taking longer to get water up to washing temperature. Will definitely check that.
posted by TinTitan at 11:46 AM on March 28, 2017

This is a question for a dishwasher repair rep, maybe even worth contacting the manufacturer about. In the interim, after you've run the Steramine tablet or taken other steps to remove the existing mold, is it convenient for you to leave the dishwasher open to air dry after washing cycles (perhaps overnight)?

Detergents and cleaning agents might make you feel like you're tackling the problem effectively, but water is the limiting factor with mold growth. If you've got the time and energy to physically scrub away the visible mold, that will work without the need for chemical agents. You can even use a fairly benign abrasive (like baking soda) with a scrubber and have just as much lasting effect as with detergents and other cleaning agents.
posted by late afternoon dreaming hotel at 11:54 AM on March 28, 2017

Best answer: Does your dishwasher have a sanitize cycle? Even if it doesn't, running a couple loads on the hottest cycle should be enough to deal with any mold. If not, I'd wonder if it is reaching the right temperature - and I'd check during the wash part of a cycle with a thermometer.

The fact that you have mold at all, strongly suggests your dishwasher isn't getting hot enough as mold should not survive normal dishwashing temperatures.
posted by ssg at 1:48 PM on March 28, 2017 [1 favorite]

For what it's worth, we never close our dishwasher except when it's running. Ditto the washing machine. We leave both doors open an inch or two to prevent mildew, and indeed we have... no mildew. I imagine this would also be helpful for mould, so would give the dishwasher a good clean and then try keeping the door open going forward.
posted by DarlingBri at 3:31 PM on March 28, 2017 [2 favorites]

Best answer: We had a Bosch dishwasher that had a bad circuit board. It pulled so much current through a small connection on a PC board that eventually the component came unsoldered. I took the door apart, removed the board and fixed it. It worked for a while - a few years - then died again. If it's not getting hot there's your culprit. You can try to fix it, buy a new board, live with it...
posted by fixedgear at 4:06 PM on March 28, 2017

I unfortunately have too much experience with this, being frugal by nature and of the (often mistaken) opinion that I can fix anything if I try hard enough. Our dishwasher had buildup inside that I tried all kinds of things on, from citric acid to bleach to vinegar. I would get rid of the surface slime (dark, like you say, and really looked sort of gelatinous and gross) and a month later it would start coming back.

You have taken the base apart and thoroughly cleaned your filter, trap and chopper, yes? Because when I did that I found the root of my slime. I probably should have ripped the whole thing out and burned it at that point, but I'm stubborn. So I took everything on that machine apart, got it to the utility sink and scrubbed and bleached it and put it back together. It took most of a day and was absolutely disgusting. There was slime hiding in the water pipes, inside the spinners, and of course the giant colony in the base of the machine. A year later my upper lip is still curling as I think of it.

A month later the slime started coming back. I think it was laughing at me. I jumped online bought a beautiful, shiny, slime free dishwasher. Reading these answers now makes me think I should have checked the heater - though bizarrely the dishes were always seemingly clean and hot at the end of a cycle. I prefer not to think about what we were injesting during that period and if I do I try and tell myself we were building our immune systems. Anything else is just too disturbing .
posted by Cuke at 7:00 PM on March 28, 2017 [2 favorites]

Response by poster: I finally had time to tinker with the dishwasher today (posting process and results here in hope of helping others in the future).

ssg: after your comment, I checked and the sanitize light was not coming on as it should after a cycle, another hint that the heating was not working properly.

sanka's suggestion to see if the heating element was broken: I checked the continuity and it was good (Used a volt meter, set to resistance/Ohms, if the element is good, should give a reading other than zero or 1, mine read 11.6). I then started the dishwasher to check if the heater was getting power and it was not, pointing to the control board.

fixedgear's suggestion of the control board: I started looking how to take the door apart to get to the control board. While searching for this, found out that it is a very common fault on Bosch dishwashers to have the heater relay on the control board fail and needing to either re-solder a new relay or replace the board.

More searching to find the part number of the control board lead me to find out that my particular model is covered under a recall for just this exact fault! I will be giving Bosch a call tomorrow morning.

I would like to thank you for all the answers and suggestions, it really helped me in stepping through the debugging, pointing me in the direction of the heating problem and randomly finding the recall. Much appreciated.
posted by TinTitan at 7:34 PM on April 2, 2017 [1 favorite]