Our house has water hammer that seems to never go away. After emptying the pipes a bunch of times I called a Plumber whose been by a bunch of times. He can’t find a root cause and installed a bunch of hammer arrestors which have helped a lot but the problem persists (the hammers are less frequent and quieter but definitely still there). He says he’s never seen anything like this, since the hammer persists even when no water is running in the house, and he couldn’t see pressure jump or drop on a gauge he installed. He basically said he is out of ideas other than to just install more arrestors or a larger expansion tank for the hot water tank. Any ideas of things he/I can look for or try? The water hammer really drives me nuts.

the arrestors need to be close to the cause to be effective.
what is the standing house water pressure?
does the house have a pressure reducing valve?
is there a toilet running?

How long, and what size, is the water main to your house? Does the hammer occur when you open a faucet or when you close it?



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What appears to be a water hammer is often pipes in the walls and attic that are not properly strapped or secured. Water hammers are often caused by quick closing valves ie Clothes and dish washer solenoid valves. As an added note: system pressures can be increased by as much as 5 times in a closed system. Make sure your pressure tank is functional and operating at the correct pressure due to pressure creep even with a pressure regulator installed.



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All great questions and thanks for asking. There seems to be no correlation between what’s running in the house and when the knocking occurs. He put the arrestors next to things like washing machine, which definitely helped but did not st all eliminate it. I’m not sure about pressure but he said he looked at a pressure gauge and didn’t see anything abnormal. There’s no toilet running. His next suggestion was to call the water company and ask if there might be some issue on their end. He also said he could put in more arrestors or a larger tank for my hot water heater but didn’t recommend it as a good use of my money and that he’s out of ideas. I just hate the sound and am worried that it will cause damage down the line. All ideas and advice appreciated.



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I live in the Los Angeles area. I almost gave up with trying to solve my water hammer problem. Had two different plumbing companies come out. They installed a water hammer arrestor at the kitchen sink and strapped some of the pipes down. This did not help.

Today, I installed more arrestors, including at the clothes washer (cold and hot) - but the problem still didn't go away. Then I read a post suggesting draining all the water from the house. The author said there are hidden air chambers in the pipes, put there when the house was built, to act as arrestors. It was suggested draining the water supply would recharge the air in these arrestors.

I followed instructions and shut off the water at the main, opened all faucets and flushed all toilets. I waited 30 minutes until no more water was dripping. Then I turned the water back on and closed the faucets (after purging the lines.) It worked! No more water hammer.

Apparently, water hammer arrestors won't work if your house pipes have not been recharged in a while.