QUESTION: My mom’s home was built in 1959. For the last year, we have heard a loud knocking any time the water from one of the kitchen, bathtub or bathroom faucets is turned off after running. It knocks four or five times and then stops. It doesn’t happen when the toilets are flushed or when the dishwasher or clothes washer are run. We have never seen evidence of a leak. Can you shed some light on what is causing the knocking?
Monica Thacker, Carmichael
ANSWER: “What you are describing is called ‘water hammer,’ but I am afraid I just don’t have enough information to make an accurate diagnosis,” says Vince McDonald of McDonald Plumbing, Heating and Air Conditioning in Sacramento.
“It is odd that the noise happens with all those faucets but not the dishwasher or washer, and that it makes noise after, rather than during, the operation of the faucets. The list of possible causes includes loose faucet washers, a bad fill valve in a toilet, and thermal expansion and contraction of the piping system. I don’t think the noise is cause for alarm. It is not likely that the problem will cause damage to the home. This sounds like a good one for an informed plumbing contractor to visit the site in person,” he says.