How can I fix my banging pipe noise ?

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The first plumber #1 that came over changed a backflow valve on the furnace. It made a small difference for a while, but then the knock came back.

The second plumber #2 came over and replaced 2 water Knock arresters. The old one may have been perfectly find, but he changed them anyway. Again, It made a small difference for a while, but then the knock came back.

I called Plumber #2 back and this time he put an expansion tank ( like the one on the heating syetem), but this one went on the domestic water system to try and take up the shock to prevent the bang. It made a small difference for a while, but then the knock came back.

Now I am into this Water Hammer for almost $400.00 and neither plumber was able to get rid of the knock.

Any suggestions would be greatly appreciated.

Thanks,

Paul

Paul...

When is the knock worst.. What fixtures are you using when the knock is loudest?

Is the sound obvious in all bathrooms? How about hot VS cold piping... worse with hot water use or cold water use or no difference when using either temp..

Let me know...

MARK

When is the knock worst.. What fixtures are you using when the knock is loudest?

Is the sound obvious in all bathrooms? How about hot VS cold piping... worse with hot water use or cold water use or no difference when using either temp..

Let me know.

The knock happens with either Hot or Cold water. All faucets, both toilets, clothes washer, but have not heard it when the dish washer is running. The sound always comes from the Furnace Area down stairs.

"Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in air chambers to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put air chambers on all bath lavatories and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will began to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out and thank you for rating my reply. TOM

Paul... try this.

Shut off the main water supply to the house and then open all the faucets including the showers and flush the toilets. Let them sit open for an hour... then turn on the water main and purge all the air out of the faucets until water flows smoothly...

Let me know if that makes a difference in the knocking over the next day or two.

I'm thinking you could have some old fashioned shock absorbers that fill up over time each time AFTER the system has been drained to work on.

Let's start here...

Sorry Tom...posted on top of you!!

Look's like Tom was thinking like I am... you can try his method or mine... both should give same result!

Mark

I did as you suggested, and the knock is not as bad. There is no knock now on the cold, but there is on the hot.

Additional Info: House age 1985 with a 1993 Peerless Oil fired furnace with hot water off the furnace as well. I did tap the heating system expansion tank to see if I would get the same sound throughout which might tell if the bladder was broken. I did get two didtinck sounds: one as thrugh it was going through metal and wated and another as though it was going through metal and air. Again, there are two new arresters and a new expansion tank on the domestic water side.

Hope this helps. I could really use some other suggestions to get rid of this hammer forever.

There may be some part loose inside or around your furnace. I would open water and let it run. Once you hear the noise, I would walk around the furnace and try to locate the spot where it is audible the most. Mark that spot. Also, put your hand on the furnace and pipes around it to see if you can locate the knock. Turn water off. Go back and carefully inspect that marked area. See what parts it has and which one could be bad. Replace the bad part.