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Banging Pipes: How to Identify and Stop Water Hammer

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  • Transcript

    LESLIE: John in Texas is dealing with some mystery plumbing noises. What can we do for you today?

    JOHN: I have a problem with my water heater, I think. When we flush the toilet, the hot-water line starts banging. My hot-water heater is in the attic.

    TOM: The question would be: what does the hot water have to do with the toilet? Probably nothing, because we don’t use hot water in the toilets. But what is happening is that when you flush the toilet, the toilet has to refill, so the cold-water line is coming on and refilling that. And that cold-water line is the same cold-water line that’s probably running into the water heater above it.

    So it sounds to me like what you have is called “water hammer,” which is caused by usually some loose pipes. And when the valve in the toilet opens to fill and then closes when it’s done, there’s some movement there. And the pipe will shake because of – the weight of the water in the pipe has a lot of inertia. And as that water stops, as the valve opens and closes, it will shake, rattle and roll the pipe.

    The other thing that will happen is sometimes, as you run cold water through the pipe – and especially with the toilet, because it’s not flushed over and over and over and over again – that temperature change in the pipe could also make the pipe expand or contract. And as that rubs against the wood, it will make some noise, too.

    So I don’t think you have a serious problem here, John. I think you probably have a water hammer issue. The first thing I would do is try to secure as many of the pipes as we can so that they’re tight and they don’t rattle. And then if it does become a problem beyond that, there’s a device called a water-hammer arrestor, which is kind of like a shock absorber for your plumbing system, that you can have a plumber install.

    JOHN: Alright. Thank you very much.

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