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Besides washing dishes first or changing detergent, are there ways to improve the cleanliness of dishes coming out of an old dish washer?

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  • yeah. clean the filter – Adam Jun 19 '16 at 22:25
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You could try adding a 2-4 quarts of vinegar to an empty load and letting it run for an extended period. Over time you can get buildup on the lines/sprayers and the vinegar will help clear out the buildup. Clearing out this buildup will provide better power for the sprayers and in turn, cleaner dishes. Of course I would run an extra cycle or two with fresh water afterwards.

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  • I do this sometimes, but in my case with dish inside the dish washer. This actually removes some of the white stain on glasses. I have seen no other side effect. I would at the very least advise against running extra empty cycles afterwards, as this seems a waste of water and energy. Vinegar is harmless, especially at the very low concentration you would have after the first cycle (once most of it has been evacuated, only traces would remain). – youen Sep 9 '17 at 16:45
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Hotter water is the biggest factor in the effectiveness of a dishwasher. In the USA, at least, this is dependent on the home hot water supply. If you have access, you can turn up the thermostat on your water heater to a minimum of 130 Fahrenheit and likely see a significant improvement. Many rentals have the thermostats set lower, typically 120 F, for liability reasons, but most dishwashers (especially the lower-end units commonly found in rental houses and apartments, which lack reheaters) don't clean well at that temperature.

The thermostat on the water heater probably won't be calibrated, so you'll have to turn it a little, wait 1-2 hours, and then run the water in a nearby tap until it's as hot as it can get before checking with a cooking thermometer. You may have to go through a few cycles of this to get the temperature right. Also, you gain little to nothing going above 135 F, and greatly increase the risk of a scalding accident if someone draws cold water while a hot shower is running or similar flow conflict occurs.

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  • I've never known a dishwasher that runs off the hot feed. They usually run off the cold to prevent you wasting 30m of cold already in the pipe ahead of the hot, which never arrives at the unit. [I'm in the UK, things may be different elsewhere] – Tetsujin Jun 21 '16 at 7:20
  • I'm in the USA and have installed a couple dishwashers. I've never seen a cabinet pocket for a dishwasher that had a cold supply. Most American dishwashers (especially low end units) don't have a water reheater, so depend on hot enough supply water. The manuals often recommend running water from the nearest tap until as hot as it gets before starting the machine, to get a hot start for best cleaning. – Zeiss Ikon Jun 21 '16 at 10:55
  • Ah, interesting, thanks for that. I'd guessed it may be a market/territory difference. We have hot & cold feeds on clothes washing machines & have to run the hot tap first to pull the cold through before starting - though the machine also has a water heater. I haven't specifically studied them since I got my last one quite a few years ago, but I'm not a professional plumber. There may be dishwashers with a hot feed & no heater in the UK, but I've never owned one or recall seeing one, all 3 I've had have been cold feeds. – Tetsujin Jun 21 '16 at 11:16

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