Knocking noise when running dishwasher

Skypathway1November 6, 2013

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 but I know kitchen has more posters. 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.

My hot water heater is also about 7-8 years old. We have plenty of hot water for showers so I'm not sure if that is the problem? No knocking when taking showers or flushing toilets.

I need to fix this problem - we can't keep running to the kitchen to run the tap when we run the dishwasher. I don't want to pay another plumber who can't fix or at least diagnose problem.

I don't want to pay for a dishwasher repair person to come unless it is the dishwasher. And if it is the dishwasher - is it a part that can be repaired or would I need to replace it? Every time I call the appliance repair person they can't fix it and I have to buy a new one - these appliances are designed now to break down and not be repairable.

Thanks in advance for any suggestions.

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Try the Terry Love forum.

    Bookmark   November 6, 2013 at 12:40PM
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Thanks catbuilder, I will.

    Bookmark   November 6, 2013 at 1:25PM
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Just an idea, by have you checked the DW sprayer arm(s) for blockage or spray problems? If sprayer water is trying to come out but is blocked some, you will hear noise in the water lines. By running your faucet concomitantly, your further reducing water pressure which will lower DW water noise.

My 2 cents worth on where I'd check. Good luck.

    Bookmark   November 6, 2013 at 1:38PM
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SparklingWater - love your name,

I had thought of that but I assumed since my dishes were clean that there was enough water spray coming out of them. Not sure how I can check that myself - but I can see your logic and maybe I do need to call the repair person.

The last three times I called the appliance repair person they couldn't fix my appliances because the manufacturers had stopping making parts so I had to buy new ones - Grrrrr I hate that.

    Bookmark   November 6, 2013 at 2:21PM
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1) make sure it's not the spray bars hitting the tops of tall dishes

2) use a dishwasher cleaner to make sure there's nothing that can prevent the spray parts from working properly.

(i've had both of these issues happen and it creates a knocking sound)

3) make sure that the plumber affixed the pipes to the walls and didn't just let them hang free in the walls. if so, every time the water rushes through, they will make knocking sounds as they vibrate against the studs and drywall.

    Bookmark   November 6, 2013 at 2:43PM
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hazeldazel, thanks for your reply.

1. I know the spray bar doesn't hit the tops of tall dishes - I've got the top and bottom racks height adjusted to accommodate the dishes etc. that I load - I can see the spray bar has plenty of room to move.

2. It has been awhile since I rand a dishwasher cleaner - I'll try that - good suggestion - thanks.

3. I believe the pipes were properly attached and we've been in the house for 14 years and this just started so I don't think that's the problem.

    Bookmark   November 6, 2013 at 9:49PM
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Ours does this and my husband thinks it is the vent to the outside that is blocked. He is going to have a plumber come look at it and see. I'll let you know if we find anything out.

    Bookmark   November 6, 2013 at 10:19PM
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Thanks kam76 - and I'm glad I'm not the only one who has this - and I can't wait to hear what you do.

    Bookmark   November 6, 2013 at 10:30PM
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We have this problem too. After a long google session, my expert (ha!) opinion is that it's "water hammer". There are instructions online that explain how to fix it, but we haven't gotten around to trying them. Maybe you'll have some luck and can give me advice!

    Bookmark   November 6, 2013 at 11:17PM
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fouramblues - I've been looking into water hammer as well and there is a gadget you can attach to your water line.

When DH is home we're going to take the bottom of the DW off so we can see this inlet valve - apparently there is a solenoid that can go bad there - I got this off an appliance forum. If that is the problem then hopefully it is fixed.

If not then adding a water hammer is the next step. I will post back with the results probably in a week or two.

And I'm glad I posted here - I don't feel so bad about this now that I see several other people have had this problem.

    Bookmark   November 7, 2013 at 11:23AM
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I had my son who is a plumber read this and he said it could be a number of things but would lean towards it being something with the DW since that is when it occurs. He mentioned the solenoid too.

    Bookmark   November 7, 2013 at 11:35AM
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You should be able to tell if the bang is from the dishwasher or the basement, right? So, which?
If basement-ish--well, you can get water hammer after 14 years because screws loosen. Go to basement & tighten all screws connecting pipes to things. We have to do this every, oh, 10 years or so. And, yes, it's usually the DW that is the first thing we hear it with.

If the noise is coming from the DW itself...well, when our arms stopped spinning (because somehow rice got into them & blocked up the little holes & yes, it took me forever to fish some a bit more out, etc.), then the telltale is that every time you open the dishwasher when it is running, the arm is in the same position. For us, it would go "clunk" and then you'd hear a whooshing noise as the water hit the door directly (the door would actually seem like it was trying to open, too).

Good luck!

    Bookmark   November 7, 2013 at 12:45PM
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meganmca, the banging is from the pipes right by the dishwasher and the noise travels into the lower level below.

I didn't know you have to tighten screws every 10 years on the plumbing - thanks for mentioning that. The plumber who thought there was air trapped in the system took apart and screwed things back together - he said everything was very clean and quality materials used.

The noise is not in the dishwasher itself and I know it's not the spinning arm. I had trapped crap in the last machine arm LOL and I know how miserable it is to clean that out - why can't they build a spin arm which is easy to take apart and clean?

    Bookmark   November 7, 2013 at 7:07PM
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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.

    Bookmark   November 7, 2013 at 11:28PM
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snoonyb, the second plumber took that apart to check the washes - everything looked good. But I didn't think that changing the position of the valve could affect it - but I guess if I partially close it, it would slow down the water flow and perhaps make it better? I'll have to test that.



    Bookmark   November 8, 2013 at 6:17PM
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It would certainly be easier then taking the DW apart, a step in the elimination process.

If it affects it at all, change the valve.
If both the DW and the faucet are feed from a single valve, invest in the fittings to separate them, therefore if one fails
you won't loose the use of the other.

    Bookmark   November 8, 2013 at 6:29PM
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