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Toilet Flush Causing Water Hammer?


Sometimes flushing a toilet can lead to some loud noises. It might be water hammer, but itwater hammer noise 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.


The standard distance is 12" and 10" or 14" are occasionally found in older homes. You can determine the rough-in on an existing toilet by measuring from the wall behind the toilet to the middle of the bolts on the base.
Posted @ Tuesday, February 21, 2012 8:41 PM by heating plumbing
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