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Water hammer at a toilet is common. Water hammer is caused by a sudden shutting off of the water. This causes a shock wave and can lead to loud noises as the shock wave rumbles around until its energy has dissipated. The shock wave is most commonly caused by an electric valve, such as a washing machine or dishwasher, but someone slamming their hand on a faucet handle can cause it too.
With a toilet, the refilling and shutting off of the water can lead to noises, but not necessarily water hammer. In a lot of cases, people who think they have water hammer, only have a toilet fill valve that is going bad. It can vibrate as water passes and then make a loud “thud” as the water is shut off. Another common source of noise can be the angle valve. As water passes through it, you can get some vibration that sounds like a whine. You can certainly replace this and the noise should stop.
If you have true water hammer, you can install a water hammer arrestor near the offending fixture. They attach to the water supply. For a toilet, you would only have one arrestor, but for a washing machine you would have both hot and cold supply locations.
Sometimes flushing a toilet can lead to some loud noises. It might be water hammer, but it probably isn’t.
Water hammer happens when the water flow is abruptly stopped. This causes a shock wave to travel the length of the piping. If the piping is not secured properly, you can get some loud banging or vibrations. This happens most often with electric valves which shut the water off very quickly…not so much with a toilet, although it can happen. In a toilet, as the float rises in the tank it gradually slows the water until it stops. For this reason it usually isn’t water hammer.
However, the fill valve can make some loud noises that people often conclude is water hammer. If you get noises when you flush the toilet, I would start by replacing the fill valve. This will probably fix the problem. Fill valves can crack and as water pushes through the valve, they can make some weird noises. You might also be getting a small “thud” when the water does stop making you think of water hammer.
Electric valves from a washing machine or even a dishwasher are more likely the culprits of water hammer. If that is the case you can install a water hammer arrestor.
I visited a customer's home yesterday after she complained about water hammer. Water hammer is a loud banging noise caused by a shock wave when the flow of water is abruptly stopped. Electric valves, such as washing machine valves. You can also get water hammer if you manually shut off a valve, for example if you slam you hand against the knob on a faucet. Here is an article on installing water hammer arrestors.
That isn't what I found at the customer's house. Instead, of a loud "banging" of the pipes, I found a repeated rumbling noise, almost like a machine gun. The vibration was enough to drive anyone crazy. This turned out to be a toilet fill valve that wouldn't shut off completely. When someone would flush a particular toilet, the water would refill in the tank as normal, but the fill valve wouldn't stop and consequently let water flow down the overflow tube and into the flush valve. The sound was the water repeatedly being turned on and off by the defective valve. This occurs more often with the old-style ballcock, the rod and float, than the newer style.
A simple job of replacing the old-style toilet ballcock with a new toilet fill valve solved the problem.
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