Author Topic: Bosch dishwasher incompatible with bosch tankless hot water. Solutions?  (Read 4342 times)

Offline adspguy

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So, I have a bosch shu9910 dishwasher and my hot water heater is a tankless bosch aquastar 1600h. As others may have noted, these tankless heaters require a minimum flow rate to activate. The 1600 requires .5gpm as a minimum. My dishwasher just misses activating the hot water heaters threshold, unless I manually cut off the hot water feed to the heater, then turn it back on again. You should see the silly dance I do to get hot water to the dishwasher! I set timers and run to the basement to open and close the feed to the water heater. When the dishwasher calls for hot water, it doesn't activate, but if I close the feed valve, then open it, while the dishwasher is demanding hot water, it activates and stays working.

I was thinking of replacing the dishwasher's water valve with a different one which would allow a slightly higher flow rate. Maybe that would be a solution. Does anyone know a replacement valve which could do the trick? Does anyone have a different solution?

Offline JWWebster

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Why not connect a Y and supply hot and cold water to the dishwasher. Warm flowing water will still be heated by the dishwasher right?
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Offline adspguy

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The problem is that the water heater doesn't turn on. When it doesn't turn on, the dishwasher will try to heat up the water itself and that takes forever. Really what I need is for the dishwasher to draw the water it uses in just a bit faster.

Offline JWWebster

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Dishwasher valves are different from other water valves. They meter the amount of water added. You go adding a different design and it won't act right. If you know you are going to activate the dishwasher maybe you ought to turn on the hot water a minute before doing so to get that tankless wonder to kick in.
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Offline adspguy

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This particular model of bosch dishwasher uses an internal float to determine when to cut off the water, rather than just a timed amount of controlled flow.

The hot water heater has no tank, it only fires up the heating element when the flow rate is above a minimum amount, in this case .5gal/min. The dishwasher draws only about .45gal/min and so it would get cold water only.

Currently I do the following:
1. run the hot water in the sink until I get hot from the tap. This fills up the pipe to the kitchen with hot water.
2. start the dishwasher.
3. run to the basement and stand next to the water heater.
4. When I hear the water flowing due to the dishwasher taking hot water, I cut the hot water  heater supply feed, and then turn it on, and the resulting surge is enough to kick the water heater into action. It then has enough flow to keep burning.
5. wait 12 mins for the next cycle.
6. repeat step 4.
7. wait 41 mins for the next cycle
8. repeat step 4.
9. breath a sigh of relief and wait until the next time I need the dishwasher.

The problem is that the dishwasher can't get the water heater started on its own all the time.

The dishwasher is not really happy trying to heat up the cold water that results from the tankless heater not running. It is just cold water.

Basically, if I could make the water surge when it starts, or flow >.5gal/min, it would be fine.


Offline JWWebster

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I wonder if you could install a 2 gallon inline electric heater to a cold water suppy line nearest the dishwasher sorta like they use in an office. Make that water heater a dedicated heater solely for the dishwasher. It is mighty funny Bosch offers This little ditty as an accompliment to that tankless wonder.
« Last Edit: November 02, 2010, 11:32:50 AM by JWWebster »
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About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
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Offline jimbo6679

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As a plumber, I can say that you have encountered one of the MANY side effects common to tankless water heaters.   Some folks love them, many folks avoid them. 

Unless one of the appliane gurus knows how to make your DW fill faster, I don't know how to help.    Have you called Bosch about the inconsistency in their product line?

 

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