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Knocking noise when running dishwasher

Posted by Skypathway1 (My Page) on
Wed, Nov 6, 13 at 11:31

Every time we run the dishwasher we get horrible loud knocking sounds in the water line as the dishwasher is pulling in water. When we run the kitchen faucet the noises stop. BTW I've also posted this in plumbing and appliances. I'm hoping maybe someone here has been through this and knows what the problem is. I haven't found anything researching online.

I've had two highly recommended plumbers to the house about this problem. The first one said it was my faucet tap and replaced the parts and for awhile it was slightly better. The second one claimed it was air trapped in the pipes, drained all the water out and fiddled around - that didn't help. He then suggested the it was the dishwasher but said he had no knowledge how dishwashers worked or what the problem could be.

I believe the dishwasher is about 7-8 years old and appears to be working properly - dishes come out clean within an appropriate time frame. The machine interior is clean - no build up of debris or clogged lines.

Has anyone here have this problem? Is it the dishwasher and were you able to repair it?


Follow-Up Postings:

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RE: Knocking noise when running dishwasher

Probably air knocking.

Check the flexible water supply line installation. The line is usually connected to a water supply line at the kitchen sink. From there, the line should be installed so the flex line loops above the connection points(both to the water supply and the unit connection points).


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RE: Knocking noise when running dishwasher

Might be the fill valve for the DW. The solenoid valve could be dropping out. Take off the kick plate cover and listen and put your hand on the valve as the DW is filling.


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RE: Knocking noise when running dishwasher

Thanks handymac - I will check the flexible water supply line.

Thanks ionized - I'm thinking that it might be the fill valve also - this weekend we take the kick plate off to check it. This was very helpful information.


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RE: Knocking noise when running dishwasher

Dishwashers don't "pull" in water. Thy have a solenoid valve that opens the line and fills the basin. Once filled the pump inside turns on and pushes the water through the sprayers for the wash cycle. It drains and repeats with fresh water for the rinse cycle, just like a clothes washer.

How do you fill the dishwasher? Often the dishes will bang when the pump/sprayers are working.

The only way I can see the kitchen tap coming into play is if you have a solenoid issue as suggested by ionized. It could be cycling open and closed and the noise is water hammer as it opens/closes. Opening the tap would reduce the line pressure and lesses the resulting water hammer as the valve opens and closes.


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RE: Knocking noise when running dishwasher

Additionally, there should be a valve controlling the DW water supply that have washers which can deteriorate, so, try changing the position of this valve.

The logic behind this, is that when you open the sink faucet the hammer stops. Well, you have changed the volume of flow when you opened the sink faucet.


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