At our kitchen sink we have a problem with the hot water flow. When the hot water is turned on full (a mixing faucet) either immediately or shortly after the water comes to a full stop simultaneously there is a knock. The water does not begin flowing until you turn off the water altogether.

We have knock arresters installed, but I don't want to pull apart the wall just to trouble shoot the hot water line arrester. Do you have any thoughts on what may be causing this problem?

The problem is also present at our dishwasher, who's supply is from the same localized valve.

Any suggestions are appreciated!

First off you don't have to go into a wall to check or recharge your air chambers, (knock arresters). I can give you instructions if you wish but it doesn't sound like a air chamber problem.
Let me first explain what has happened and then tell you how to fix it. If your heater isn't flushed on a regular basis it will build up minerals on the heater floor. After a time this mineral build up will find its way into the hot water system.
. The first fixture making a draw, (your sink) sucked the debris up into the supplies blocking the valve. The sound you hear is the crud hitting the valve and stopping suddenly.
Since you failed to tell me the brand and type, one handle or two knobs, I can't get specific but here's what you must do.
First shut the water off at the angle stops located in the cabinet. Open up the faucet and clean the crud out of the seats or, in the case of a one handled valve, the inlet ports of the cartridge.
Next, place a pan over the open valve body to prevent splash and turn the angle stops back on for a few seconds to flush out the supplies. You may now reassemble the faucet and test.
So that this doesn't happen again from minerals building up in your heater let me start you on a monthly maintenance schedule to prevent it.

For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Let me show you how. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Now flush out your hot water lines on ALL fixtures. Now pull each aerator and clean the screens. Be sure you put them back togather the same way you took them out. Don't forget to flush it out every month. Your heater will thank you for it.
Good luck, Tom

OR, by email:
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This is the message:

Tom,
Thanks for the reply to my question posting! I have a bit more information,
Just wanted to pass it by you to see if there is any different diagnosis or
Additional items I should look into!

The faucet is a Grohe kitchen faucet with a single mixing handle. The entire
House was re-plumbed in copper 20 months ago, by yours truly! In addition the
Water heater is new.

I originally didn't think I would need to flush the water heater until it had
Been 24 months given the water is from a municipal water district, san
Francisco, but this seems to make a lot of sense! I honestly got busy continuing
On finishing the renovation and never read much beyond the install in my handy
Book. Do you think the new piping allows for more mineral build up, given
Little is getting stopped in the system? Just curious!

I'll try your suggestion this weekend, tough to take care of in the evenings but
I will let you know the result!

Do you think I should take a similar look at my maytag dishwasher? It is fed
From the same angle stop as the kitchen faucet, I just don't know where to look
For the clean out - I'll have to look into the manual!

Thanks for your help!

If you have a moment I have another question, my wife noticed a sweet taste in
The cold water that comes from our bathroom sink, faucet. It is a two handle
Kohler faucet. I didn't notice it until recently, so it took me a few months
More to notice, but she noticed about 12-14 months after I completed the work!
Any ideas? I don't think it could be flux, given the length of time and it does
Not have the same taste out of the hot water on the same fixture or any other
Fixture in the house?

Your comments are grately appreciated!

Dan

Hi Dan,
Sorry about the delay. I know of nothing with a sweet taste that could get into your lavatory faucet. One possible explanation is that her toothbrush got next to the faucets spout and left a bit of toothpaste on it and that's what she's tasting. By now it should be gone. Good luck, Tom