How to Repair a Water Hammer
A water hammer is a sharp banging noise that you'll hear after you flush a toilet or turn off the water. It can be one loud bang when a faucet is shut off quickly or a series of hammering sounds when a toilet is filled and shuts off slowly.
This may be a job for a professional plumber; however, there are a few actions the do-it-yourself can take to solve the problem first. If they work, you won't have to listen to the hammering any longer, and you will have saved yourself the expense of a costly house visit from the local plumber as well.
Shut off the main water supply, which is normally located in the basement. Turn the valve clockwise to close it.
Start in the basement, and open all your faucets and spouts and flush all toilets. Make sure all the water has been drained from the pipes throughout the house. Once all the water is out, turn off all the fixtures.
Reopen the main water valve. Starting upstairs, turn faucets and spouts on, letting the water force all the air out of the pipes. Continue opening spouts on each floor until you have reached the basement.
Open a faucet all the way, and shut it off quickly to see if the water hammer has been eliminated.