It may seem like something out of a ghost story, but there’s usually a simple explanation for why your home’s plumbing system makes a knocking noise. Sometimes it’s due to water pressure issues, while other times it’s due to loose pipes or a faulty valve. If you notice loud banging taking place when you turn on the water, or at any time of day, here are some possible explanations.
Loose Supply Pipes
Over years of use, the pipes that supply hot and cold water to your faucets can become loose from the straps that secure them to your house. The water pressure that passes through the loose pipes causes them to bang against the wall, causing that knocking sound you hear. This problem only occurs while the water is running, so if the banging noise stops the moment you shut off your water, it’s a good indication that loose pipes are the culprit.
If the troublesome pipe can be reached, you can fasten the strap to the wall yourself, being careful not to do so too tightly so the pipe can be allowed to expand and contract due to changing water temperatures. If the pipes are within a wall, you may be able to get rid of the knocking noise by stuffing padding or foam at each end where the pipe enters and exits the wall.
High Water Pressure
If the water pressure is too high, your pipes may rattle around regardless of how well they’re secured to the wall. If this is the case, you’ll notice that, as with loose pipes, the noise only occurs while the water is running. The noise you hear, however, will be more of a quiet tapping sound rather than a full knocking. Your water pressure should be between 40 and 80 psi. If your cold water pressure is over 80 psi, you might want to install a pressure reducing valve. If your hot water is causing the problem, try turning the temperature down a bit. If that doesn’t work, consider installing a hot water expansion tank. This will absorb the excess pressure, protecting your pipes.
If you notice a loud knocking sound only when you shut the water off – and not when it’s running – your plumbing is probably suffering from water hammer. Water hammer is caused by a valve suddenly shutting, forcing water to bang into the valve and the water in front of it. If your home was built before 1960, this could be a very easy problem to solve. Older homes come with air chambers installed that can become filled with water. By shutting off your water, and running all your faucets at once, you can drain the excess water from your pipes, stopping the water hammer. Newer homes come with water hammer arrestors which act as shock absorbers for your pipes. If your arrestors have failed, you’ll have to call in a professional plumber to install new ones.
Knocking noises in your plumbing are rarely as bad as they sound. Once you’ve analyzed the problem, you can pinpoint the solution and cure your home of all of its annoying knocking.