Hearing unexplained knocking noise or banging noise in your plumbing system, especially when no taps are running, can be disconcerting, particularly if you have a pressure regulator for noisy water pipes. This guide explores the common causes of these sounds, how to determine whether they are harmless or concerning, and what you can do to resolve or prevent them in your home.
What Causes Knocking Sounds in Pipes Without Water Flow?
Unusual pipe noises when no water is being used in plumbing pipes can stem from a variety of factors:
Thermal Expansion:
When warm water passes through copper pipes, the surrounding building materials can influence how the material expands. As the pipes cool, they contract, and this process can cause them to rub against surrounding structures or brackets, producing knocking or clicking noises.
Loose Pipe Brackets or Clips:
Pipes that are not securely fixed in place may shift or vibrate as they expand, especially if affected by a water pressure regulator contract, or respond to residual pressure in the system.
Trapped Air in the Pipes:
Air pockets within the plumbing system can move unexpectedly, creating intermittent knocking or thumping noises from vibrating pipes, which can sometimes be mitigated by adding air chambers.
Residual Water Pressure:
Pressure that remains in the system after water use can sometimes cause small movements or valve responses that lead to a loud banging noise.
Automatic Appliances:
Some appliances, such as dishwashers, water heaters, or refrigerators with ice makers, may draw water independently, resulting in short bursts of pressure that produce loud noises and audible sounds.
The specific sound—whether dull, sharp, rhythmic, or intermittent—may vary depending on the type of pipe (metal or plastic pipes), its location, and the cause of the disturbance.
When Is It Normal, and When Should You Be Concerned?
Some knocking sounds in plumbing systems, including noisy pipes, are normal and pose no risk. However, others may indicate a more serious issue.
Normal situations include:
Occasional clicking or tapping as hot water pipes cool down and may be a relatively simple fix.
Minor noises after large water usage, such as a hot shower or in the laundry room during a cycle.
Concerning signs include signs of a banging noise,
Repeated, loud knocking or banging with no water usage
Noises that persist or worsen over time
Knocking accompanied by signs of water damage, leaks, or damp patches
Sudden changes in water pressure or sudden rush of temperature when taps are used
Persistent or loud banging sounds from pipes when water is not running, especially when it occurs frequently and without any identifiable water use, warrants further investigation.
Where Are These Noises Commonly Heard?
Knocking pipe sounds often originate in the following areas:
- Inside walls adjacent to bathrooms, kitchens, or laundries
- Ceiling cavities or roof spaces, where vertical water pipes are located
- Floors and subfloors, particularly in double-storey homes
- Near hot water systems, where pipe expansion is common
You can try to identify the source by noting the timing and location of the sound, or by using sound detection tools to trace back to visible water lines . Listening carefully during quiet times, when noisy water pipes might be more noticeable such as early morning or late at night, can help you narrow down the source.
Could It Be Water Hammer Without Active Use?
Water hammer typically occurs when water flow is stopped abruptly, causing a pressure shockwave that reverberates through the water hammer pipes, and you may need to fix water hammer . While usually associated with turning off taps, a similar effect can happen without active use.
Causes may include:
- Faulty or partially closed valves
- Residual system pressure
- Appliances with fast-acting solenoid valves
Even a minor pressure fluctuation due to a faulty pressure reducer can cause pipes to move slightly, mimicking the sound of a traditional water hammer. In older or poorly installed systems, this can be more pronounced.
DIY Checks to Identify the Source
Before calling a professional plumber, you may wish to perform a few simple checks:
Inspect visible pipes for signs of movement or loose brackets
Listen for patterns, such as noise occurring after hot water use or during cooling periods
Turn off the main water supply, then reopen it after a few minutes to reset pressure and release air
Test appliances to see if any are triggering the noise during their cycles
Check tap washers and valves, as worn or vibrating components can cause minor banging or rattling
If your home has a water pressure-reducing valve, verify that the setting is appropriate for residential use (generally between 350 and 500 kPa in Australia).
Fixes You Can Try at Home
There are a few safe and straightforward steps you can take to resolve minor knocking pipe issues:
- Secure loose pipes using pipe clips or brackets. Adding rubber padding between the pipe and structure can help absorb vibrations.
- Insulate exposed pipes, particularly those near joists or in roof spaces, to reduce expansion-related noise.
- Drain and refill your plumbing system to clear air pockets:
- Shut off the main water supply.
- Open all taps (hot and cold) to drain the system.
- Once drained, close the taps and reopen the mains.
- Replace tap washers if they appear worn or loose, as they may cause internal vibration.
- Lower your water pressure, if it is above recommended residential levels.
If these steps do not resolve the issue, or if you suspect a hidden fault, further professional assessment is recommended.
When to Call a Licensed Plumber in Australia
Some plumbing issues go beyond simple DIY fixes. Contact a licensed plumber if:
- The noise is persistent, loud, or increasing in frequency
- You cannot locate the source or resolve it with basic checks
- Your home has old or original plumbing, particularly metal pipes
- You see signs of leakage, water stains, or mould
- Water pressure appears unusually high or fluctuates significantly
A licensed plumber will be able to perform a full inspection, identify the root cause, and carry out repairs in accordance with Australian plumbing standards and local regulations.
Preventative Tips to Avoid Future Pipe Noises
To prevent knocking pipes in the future, consider these long-term strategies, including installing water hammer arrestors and checking your sprinkler system:
- Ensure all pipes are correctly supported and clipped, especially in areas with long pipe runs or bends
- Use insulation sleeves or lagging on hot water pipes to minimise expansion noise
- Have your plumbing system inspected every few years, particularly in homes older than 20 years
- Check valves and tap washers regularly to ensure they are functioning properly
- Install a water hammer arrestor, especially if you use appliances with fast-closing valves
Keeping your system well-maintained is the best way to avoid disruptive noises and protect your home from hidden water damage.
Frequently Asked Questions (FAQs)
Why do pipes knock when water is not running?
This may be due to thermal expansion, trapped air, residual water pressure, or automatic appliances drawing water, leading to banging pipes .
How do I fix a water hammer when no water is running?
Try draining the system to remove air, securing loose pipes, or adjusting your water pressure, which may eliminate whistling sound . If unsure, consult a plumber.
Should I worry about knocking pipes?
Occasional noises may be harmless, but repeated or loud knocking due to high water pressure could indicate a plumbing fault that requires attention.
Why do pipes clunk when water is shut off?
This is usually a result of water hammer, where sudden stoppage of flow creates a pressure shockwave inside the pipes.
Why does my plumbing make noise even when not in use?
Appliances, valve issues, or thermal contraction after hot water use may cause residual movement and noise in warm water systems .
Can water hammer occur even if no one is using water?
Yes. Valves or residual pressure can trigger movement and banging sounds, even in the absence of water flow.
Is it safe to ignore banging or knocking pipes?
No. Unresolved plumbing noise, especially loud banging, can be a symptom of hidden faults, which may lead to leaks, water damage, or increased utility bills.
Conclusion
Knocking pipes are not just an annoying sound—they can be a sign of hydraulic shock and underlying issues in your plumbing system. Whether it’s thermal expansion, hammering sound rattling noise from air in the lines, or pressure irregularities, taking the time to investigate and address the cause is essential. While some fixes are simple, persistent or worsening issues should always be assessed by a qualified plumber. Regular maintenance, including checking for sediment buildup, and a proactive approach can help ensure your plumbing remains quiet, efficient, and reliable.
