What Causes Water Hammer?

What Causes Water Hammer?
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Do you hear loud banging sounds coming from your plumbing pipes behind the wall when you turn the water faucet off – or when the water cycle ends in your washing machine or dishwasher? Or at random times? If you’ve been living with this situation for a while, you may be wondering if you need to do anything about it, or call a plumber.

This annoying phenomenon has a name: water hammer. Cut to the chase, it does need attention. The good news is that repairing the cause(s) of water hammer is relatively easy in most cases. The bad news: Allowing water hammer to continue can eventually result in leaks and even a burst pipe – necessitating a more extensive repair and possible damage to your home.

As we covered in our blog post – “What Should Homeowners Know About Plumbing?” – knowing about water hammer can help you maintain your home’s plumbing in top condition and prevent serious problems.

More Than an Annoying Noise

While many plumbing problems occur unseen until it’s too late – such as behind-the-wall or underground leaks – water hammer at least has the decency to announce that you have an issue. Our colleagues at Benjamin Franklin Plumbing describe it as follows:

“When you hear water hammer sounds in the home, this means the water in your plumbing pipes is under pressure. When it’s rushing through an open faucet and you turn it off suddenly, the flow of water slams into the closed valve, creating a hydraulic shock. The impact can cause all sorts of problems, including broken pipes, loose fittings, and damage to water-connected appliances.

“The shockwaves from water hammer can also cause your pipes to physically move from the jolt. If they’re not adequately secured to the joists in your home with suitable pipe straps, the moving pipes may bang against your walls, making even more noise and increasing the odds of damage.”

Older homes are more likely to experience water hammer. As an article in PlumbingToday notes, “Homes built before the 1960s usually have air chambers. Air chambers are basically T-sections of pipe that contain air and act as shock absorbers. However, over time the air in the chamber can become displaced by water.

“Homes built since the 1960s should have water hammer arrestors installed. Water hammer arrestors are the modern replacement for air chambers. They are spring-loaded and rarely fail.”

Also, says Tom Bigley, United Association (UA) Director of Plumbing, older homes that have pipes with 90-degree angles are more prone to water hammer.

Water hammer locations and causes

Water hammering can be caused by waterlogged air chambers, clogged chambers or excess pressure in the plumbing system. It can also be the result of a valve or pipe clog, which may produce a staccato banging sound.

However, the location of the noise or when it occurs can indicate the cause. Here are the most common, according to PlumbingToday:

Running hot water – A clicking or knocking sound starts soon after turning on a hot water tap, which may continue up to several minutes after turning it off. This could be caused by poor installation of your home’s CPVC (chlorinated polyvinyl-chloride) water lines. Because they expand with heat, CPVC lines that have been run through holes or areas that don’t leave enough room for expansion will make the telltale noise.

Solution – Find the affected pipes and give them adequate “breathing” space. We recommend hiring a professional plumber as opposed to taking the DIY approach, as this repair will most likely involve cutting into walls and/or relocating the piping.

Shutting off a water supply, either cold or hot water – This produces the true water hammer sound. It occurs when a water valve is suddenly shut off. All the water that was running crashes into the valve, shaking your pipes and creating the knocking noise. This may occur when you flush the toilet, your washing machine finishes filling with water or when your yard irrigation system shuts off. Over time, this violent motion shakes the pipes loose from their joints, causing leaks.

Solution – There is a five-step DIY fix for homes built before the 1960s, as follows:

  1. Shut off the water to your home at the main.
  2. Open the highest faucet in your home.
  3. Open the lowest faucet (it’s usually outside) and let all the water drain out. At this point the air will be “refilled” in the air chambers.
  4. Turn the lowest faucet off and turn the water main back on.
  5. Let the top faucet run until it stops sputtering, then turn it off.

As stated previously, homes built since the ‘60s probably have water hammer arrestors installed. Piston-style arrestors have moving parts, and need to be replaced. Stainless steel constructed water hammer arrestors seldom, if ever, need replacing.

Running cold water – A knocking sound that occurs after turning on the cold water tap may be caused by high water pressure. When water flows through a pipe too fast, it bounces off the sides and into itself, which shakes the pipe. The shaking pipes can rattle against walls and other pipes. To learn if this is the issue, check your home’s incoming water pressure with a water pressure test gauge. Attach the gauge to the hose bib that is closest to your water main. Make sure no other water is being used in your house, then turn on the hose bib completely. Your water pressure should read 40-80 PSI. If the reading is higher, you’ll need to call a plumber to add, replace or adjust your home’s pressure reducing valve (PRV).

No water is running – Hearing sounds from the pipes even when no water is running indicates sediment buildup in your water heater. In this situation, the noise is steam bubbles escaping the sediment that has built up at the bottom of the water heater tank – similar to how boiling water in a covered pot on the stove starts pushing up the pot’s top.

The unit’s heating element is at the bottom of the tank, where the sediment has settled and mixed with water. The sound can be loud enough that the reverberations carry and make it seem like the knocking is coming from the pipes in the wall, even though it isn’t.

Solution – If you have the right hands-on know-how (as opposed to watching YouTube videos), you can flush your water heater yourself. PlumbingToday provides step-by-step instructions, but we strongly recommend you hire a professional plumber if this is not in your wheelhouse.

DIY or call a pro?

While the above list gives the recommended course of action for each situation, we want to emphasize that your level of confidence in your ability to correctly identify the cause of your home’s water hammer – and remedy it – needs to be considered. For example, in the case of troubleshooting the “shutting off the cold or hot water” scenario, you can’t be expected to know whether your older home definitely has pipes with air chambers – or if your newer home’s pipes have piston-style or stainless steel water hammer arrestors. Only a professional plumber can make an accurate diagnosis and repair.

Our team of master plumbers at Adams and Son Plumbing recommends taking the cautious approach. If you are not mechanically inclined, or don’t feel that you have the physical capability to do the job, you should not go out of your comfort zone – even if you may be willing to risk it to save money. A botched plumbing project will ultimately cost more – not only in fixing the original problem, but in repairing the additional damage that occurred during the process.

When in doubt, contact us! We are a family-owned business with over 60 years of providing residential and commercial service throughout Central Florida. A state-certified plumbing contractor, we have over three generations of master plumbing experience. Call today to learn more and schedule a service appointment to keep your home’s plumbing in top condition. We welcome the opportunity to become your dependable family plumber!

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