No hot water to dishwasher from thankless water heater

Discussion in 'Tankless Water Heater Forum' started by Doug Whetstone, Jun 19, 2021.

  1. Doug Whetstone

    Doug Whetstone New Member

    Jun 19, 2021
    Jeff City, MO
    It takes a long time for the hot water from the tankless unit to reach the dishwasher, consequently, the dishwasher isn't getting the dishes clean. Can I put a mini tankless unit in line and under the sink to 'preheat' the hot water going to the dishwasher? Or maybe just use the mini unit on the cold water line to just supply the dishwasher? Also, I'm replacing old copper pipe with PEX. Do I need to insulate it?
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    There are dishwashers with hot water heating built in. It may be an option on yours. What model do you have?
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    TO overcome the time it takes to purge the hot water line and get hot water to a remote location, some people put a small electric tank close by and feed it from the hot line. This puts hot water there nearly immediately, and if it is sized properly, about when it runs out of its hot water, the hot water from the tankless arrives to refill it, so it doesn't need to run much. A small electric tank is generally fairly well insulated and won't take much power. An electric tankless capable of raising the temperature enough for a DW will require some significant power. Some small electric tanks will run on 120vac. Unless you're running DW loads back to back, the slow recovery isn't an issue.
  5. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    A dishwasher needs 120 degree water to dissolve the detergent and to sanitize, 140 degree. As Terry suggest, most new dishwashers do have built in water heaters and the more important, it maintains the temperature during the wash cycle. A point of use WH do work well but the water temperature will not be maintained during the wash cycle. I have a BOSCH DW and it heats the water during the wash and rinse cycles. It has a Sanitize option button, Whirlpool has a High Heat option.

    Sometimes the complaint of the dishwasher not cleaning is the spray arm nozzles get clogged with food debris. My daughter-in-law had the complaint and how they need a new dishwasher. After few hours taking apart and cleaned out the nozzles, mosty paper residue from labels that are put on dishes or glasses, it performed like new. Many new DW's, i.e. BOSCH, have a filter screen inside the tub to prevent the nozzles from clogging up.

    So your options are replace the dishwasher or use a point of use on the hot water line. You can also tee off of the from the WH to feed the sink faucet. Insulating any pipe is always a good idea if it is in unconditioned space.
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