Recently I had a small opening made on the wall connecting my kitchen and dining area. There were two pipes, one vent and the other carrying water which were both cut ( initially they were going straight up) and they were re-routed to allow for the small opening. One week after that I have been having water hammer. After any faucet or flush is turned off the pipes starts vibrating vigorously. I read some of the site where it says to close the main water supply and then let the faucet drain at the lowest point and also open up other faucets, then close them and open up main water line to allow water to fill up where there might have been air. I did that but I think my main water line doesn't shut off completely, is it why the problem did not resolve? The handy man said he has similar problem when he tried to cut off the pipe, was not able to shut off the water completely. Do you think has to do with the pipes that were cut and re-routed? What should I do? This problem has never occurred before! How do I get rid of this noise? Some times it even comes again much later after the faucet has been closed. Please help!

It has nothing to do with the vent and everything to do with the supply line. First, get a better handyman to replace your main shut off. If you can't close it completely now you won't be able to cloise it any better during an emergency. The hammer is due to air in the supply lines. Most likely. Besides draining the system you should consider adding anti-hammer devices that can be attached just before the faucet valve, usually below a sink.

Thanks for your help. I think we already have arresters installed near the faucets, that is anti-hammer right or you mean something else? Also, how would the main line not shutting off completely cause this problem? It must have been like this all the time but we never had problem with water hammer. But I do agree we should get it fixed for empergencys. But for now do you think fixing the main line has anything to do with it? How does the air get in?
Thanks again

Back in the 60's we were required to to put shock absorbers,(air chambers) on all bath lavatorys 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 begain 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 on a two bathhiome. 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 TOM

I tried what you told me. The noise has gone down but still makes some noise. I was not able to completely shut of the main water valve when did what you recommended, do you think the problem persist because of that. Can there be ice in the pipes?
Also, today when I ran the dishwasher there was a burning smell in it, is there anything I can do to check if the water connection to dishwasher is OK after all the stop angles I cleaned, do you think that affects the dishwasher?
Thanks much

First off, replace the house shut off, It's difficult to drain the air chamber if you have water seeping into the angle stop. Then do the procedure again.
This should have no effect on your dishwasher. That sounds like a separate problem. Good luck, Tom

Speedball and I both indicated to replace the main shut off first. You are draining and refilling the system at the same time. The fact that you see an improvement shows you are on the right tack, just not there yet. Get someone to fix the main and that might well require that the city shuts your supply off at the street during the replacement.

That burning smell isn't related. It is probably one of two things. You could have a belt slipping in the transmission but that normally makes a pretty good squeal. Debris falling on the heating element is a more likely culprit.

No to be an alarmist, but did the person who re-routed the water piping strap the pipes as needed, or did he leave them dangling?

Another possibility -- If the shut off valve that won't shut off is the type with a rubber washer and brass seat, then the hammering could be related to a worn or missing washer.

Get that shut-off replaced, if possible, have the plumber replace it with a full port ball valve, which will be much easier to shut off/turn on than a gate valve.

Just my two pence.

Thanks so much for all your help. I'll get the main shut of valve as you all have mentioned. And then see if the problem remains.
Thanks again.