Nasty water hammering after some changes to the home plumbing

Old 11-22-21, 08:31 AM
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Nasty water hammering after some changes to the home plumbing

So I removed this dechlorinating device that came with my home and coupled the piping together, changed the whole house filter, and drained my hot water heater. Now what I'm noticing is some really nasty water hammering when running the dishwasher and laundry washer. Mind you that the kitchen sink, which is connected to the dishwasher, doesn't have this problem when running, and the laundry already has water hammer arrestors installed on both lines (I think I purchased two of these:

I checked the hot water heater and noticed it sounds like there's hammering inside the heater when the hammering is going on even though you really hear it while in the kitchen. The kitchen sink water comes out irregular when this is happening. I was thinking about installing another water hammer arrestor under the kitchen sink but wanted to get your take on it. What do you think?


Old 11-22-21, 09:20 AM
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You talked about a lot of stuff. When and where exactly is the water sound occurring?

If your water heater is gas it is common for them to make a hammering/thumping sound when the burner is on.
Old 11-22-21, 09:29 AM
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Are there not pipe clamps @ the recommended interval? Perhaps the present interval worked so far?

Maybe a loose washer pulsing the flow rate
so the plumbing changes & the new hammering are a coincidence?
Old 11-22-21, 09:54 AM
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Without seeing the before and after layout, it is difficult to determine what affect the re-plumbing of either the hot or cold or both supply lines has on the water hammer, after removing the dechlorinator. Arresters are not usually needed at a sink because the water shut off valves are manually operated resulting in a gradual stop to the water flow. The valves on the water lines to a dish washer and clothes washer are electrically operates using a solenoid which is fact acting compared to a manual valve. My recommendation is to install an arrester on the hot water line to the dish washer. The Oakley arrester you referenced look as if the shock absorber section is removable. Does the manual say it is adjustable? I am not familiar with the unit. Are the plumbing pipes very secure where the arresters are attached?
Old 11-22-21, 09:59 AM
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Water hammer typ occurs when there is a long run of pipe and you have a fast shutting device, faucet or solenoid valve.

The hammer you think you are hearing in the water heater is probably just the shock wave traveling through the lines, there is nothing shutting off inside the water heater.

You need to look at what the layout was before and what you have now and figure out what changed and go with arrestors at that location.

We don't know any of that information.
Old 11-22-21, 10:47 AM
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What you are hearing is probably just air in the lines. Every single fixture needs to be run for a while to get all the air out of the lines. The first time you flush a toilet or run a washer or dishwasher it will make some noise as the air exits the line. The water may also be discolored as a result which is why you usually let them run for a while to flush out that dirty water.

Water hammer is a different problem.
Old 11-24-21, 01:14 PM
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Can this damage my home plumbing? I'm asking because of the holidays and i can't react to fixing this as quickly as I'd like. We've run like three dishwasher cycles and three loads of laundry.
Old 11-25-21, 05:53 AM
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For best results, water hammer arrestors need to be placed just before the valve whose closing produces the water hammer.

Water hammer can cause pipe joints to loosen and leak, not ruling out cracking of solder joints in copper plumbing. Water hammer can damage valves and parts inside dishwashers and other water-using appliances.

An elbow some distance from fastenings against building structure (as opposed to pipe hangers) can magnify water hammer sound.

Water hammer arrestors you make yourself from lenghths of pipe can become waterlogged.

Do not drain a water heater without first turning off its heat. The vacation setting is not low enough. All-electric heaters must have the breaker turned off. Do not start up the water heater again until after you have seen water gushing non-stop for a minute from a hot faucet upstairs.

Last edited by AllanJ; 11-25-21 at 06:09 AM.
Old 11-28-21, 06:21 PM
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Can you clarify, are you hearing:
A loud 'BANG' when water is turned on or off quickly - water hammer
Or a jackhammer sound that happens when the water is running?

The first is usually caused by too-high pressure, while the second is most often caused by a loose or degraded washer in a valve or PRV. Some more details we might be able to help more.
Old 11-30-21, 10:13 PM
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We installed a water hammer arrestor on the pipe leading into the dishwasher. Here's the product we used:

Ran a single dishwashing cycle and no water hammering, so that may have done the trick. I'll come back if needed.

Thanks for your help.

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