If your Navien tankless water heater is making a knocking noise, it can be worrying. Many homeowners trust Navien for efficient hot water, but strange sounds from the unit often signal a problem. Ignoring these noises could lead to bigger issues, like expensive repairs or even a complete breakdown. Understanding what causes knocking sounds, how to fix them, and how to prevent them can save you money and trouble in the long run.
This guide will help you get clear about why your Navien heater knocks, what steps you can take, and when you need a professional. You’ll also learn how to keep your tankless water heater running quietly and efficiently for years.
Whether you’re a DIY enthusiast or a concerned homeowner, this article covers all you need to know about the knocking noise in Navien tankless water heaters.
What Is A Knocking Noise In A Navien Tankless Water Heater?
A knocking noise is a repetitive, tapping, or banging sound that comes from inside your tankless water heater. Unlike normal operational sounds like water flow or soft humming, knocking is loud and distinct. Some describe it as a hammering or popping sound, especially when the heater turns on or off.
This noise can happen at different times:
- When you turn on hot water
- As the heater starts or stops heating
- While the unit is running
The sound often comes from inside the unit, but sometimes you can hear it through the pipes in your walls. It’s important to recognize these sounds early. A knocking noise is almost never “normal” and usually means something needs attention.
Common Causes Of Knocking Noise In Navien Tankless Water Heaters
Let’s look at what typically causes knocking in Navien units. Knowing the cause helps you decide the right fix.
1. Water Hammer
Water hammer is a common plumbing issue. It happens when a valve closes quickly and water suddenly stops or changes direction. This sends a shockwave through your pipes, making a loud bang or knock.
Tankless water heaters, including Navien models, often trigger water hammer because they open and close valves rapidly to control water flow. If your pipes aren’t properly secured or lack air chambers, water hammer can be louder.
2. Limescale Or Mineral Buildup
Hard water contains minerals like calcium and magnesium. Over time, these minerals collect inside the heater’s heat exchanger. This limescale buildup can cause:
- Uneven heating
- Overheating of certain spots
- Strange noises as water boils under the scale
A knocking or popping sound often means mineral deposits are causing the water to heat unevenly, leading to local boiling and tiny steam explosions inside the unit.
3. Loose Or Vibrating Pipes
Your home’s hot water pipes may not be firmly attached. When the heater starts or stops, the sudden change in water pressure makes loose pipes bang against walls or framing. This can sound like knocking or rattling, especially in older homes.
4. Faulty Flow Sensor Or Valve
A faulty flow sensor or a sticky valve inside your Navien heater can cause irregular operation. The unit may open and close valves rapidly or at the wrong time, creating knocking noises. Sometimes, worn-out solenoid valves or check valves cause this effect.
5. Air In The System
Air trapped in your water pipes or inside the heater can cause knocking. Air bubbles move quickly and suddenly through the system, making tapping or knocking noises. This often happens after plumbing work or if the heater was recently installed or serviced.
6. Blocked Or Dirty Heat Exchanger
If the heat exchanger is blocked by debris or sludge, water flow becomes irregular. This can cause pressure changes and localized boiling, resulting in knocking or popping sounds. Blocked heat exchangers also reduce efficiency and can damage your heater over time.
7. Expansion And Contraction Of Metal Parts
When metal heats up or cools down, it expands or contracts. In tankless heaters, this can cause “clicking” or “knocking” as metal parts move slightly. While a small amount of this is normal, loud or repeated knocking suggests a problem, like overheating or loose mounting.
8. Incorrect Installation
Improper installation can cause various noises. If the heater isn’t mounted securely, or if pipes are misaligned, vibrations can create knocking sounds. Using the wrong type of mounting hardware or skipping vibration pads makes the problem worse.
9. Gas Supply Issues
For Navien’s gas models, inconsistent gas pressure or a dirty burner can cause incomplete combustion. This leads to “puffing” or knocking sounds during startup or operation. It’s less common, but important to check, especially if the noise is new or comes with other issues like a pilot light going out.
10. Sediment In Water Lines
If your home has old pipes, rust or sediment may collect in the lines. When the heater starts, this debris can move quickly, hitting valves or the heat exchanger, making a knocking sound.
How To Diagnose Knocking Noise In A Navien Tankless Water Heater
Pinpointing the cause is key before you try to fix the noise. Here’s how you can diagnose the issue step by step.
Step 1: Identify When The Noise Happens
Listen carefully and note:
- Does it happen only when hot water is used?
- Does it happen at startup, shutdown, or all the time?
- Is the noise inside the heater or in the walls?
This information helps you focus on the likely cause.
Step 2: Check For Water Hammer
Turn on and off the hot water quickly. A single loud bang usually means water hammer. Try the same test with cold water. If you hear the noise with both, it’s probably a plumbing issue, not the heater itself.
Step 3: Inspect For Limescale Buildup
Look for these signs:
- Longer heating times
- Fluctuating water temperature
- Reduced water flow
- Knocking or popping during heating
If you live in a hard water area and haven’t descaled the unit in a year, limescale is likely.
Step 4: Examine Pipe Mounting
Tap on your visible pipes. If they move or rattle, they may be loose. Listen near pipe bends or where pipes enter walls. Knocking from these areas points to pipe movement.
Step 5: Check For Air In System
If you recently did plumbing work, or if you hear gurgling along with knocking, air is probably trapped. Bleed the air out by opening all hot water taps for a few minutes.
Step 6: Test For Faulty Components
A service technician can check:
- Flow sensors
- Solenoid valves
- Heat exchanger for blockages
If the noise comes from inside the heater and doesn’t match the above, internal parts may be failing.
Step 7: Review Installation
Compare your installation to the Navien manual. Look for:
- Missing vibration pads
- Incorrect mounting
- Pipes not straight or under stress
Even small mistakes can cause big noises.
Step 8: Check Gas Supply (for Gas Models)
If you have a gas model, check for:
- Irregular flame
- Soot buildup
- Delayed ignition
These can all cause strange noises, including knocking.
Step 9: Inspect For Sediment
Remove and inspect the inlet water filter. If you see sand, rust, or dirt, the knocking could be from sediment moving through the unit.
Fixing Knocking Noise In Navien Tankless Water Heaters
Once you’ve found the likely cause, here’s what you can do. Some solutions are simple, others need a professional.
1. Fixing Water Hammer
- Install a water hammer arrestor: This device absorbs the shock and stops pipes from banging.
- Secure loose pipes: Use pipe clamps or insulation to keep pipes from moving.
- Check shut-off valves: Slow-closing valves reduce water hammer.
Most hardware stores sell water hammer arrestors. They’re easy to install on exposed pipes near your heater.
2. Removing Limescale Or Mineral Buildup
Descale your heater with a vinegar or commercial descaling kit. Here’s how:
- Turn off power and water supply to the heater.
- Isolate the heater using the service valves.
- Attach hoses to the service ports.
- Pump vinegar or descaler through the unit for 45–60 minutes.
- Flush with clean water before reconnecting.
This maintenance removes mineral deposits and quiets knocking from limescale.
3. Securing Pipes
- Add pipe straps or brackets every 4–6 feet along long runs.
- Use foam pipe insulation to cushion pipes.
- Check behind walls if possible, especially near the heater.
Securing pipes stops them from hitting framing during water pressure changes.
4. Repairing Faulty Valves Or Sensors
Some parts inside your Navien heater can wear out:
- Solenoid valves
- Flow sensors
- Check valves
If you suspect a faulty part, call a certified technician. Replacing these parts requires special tools and knowledge.
5. Bleeding Air From The System
- Open all hot water taps in the house.
- Run water until you hear no more gurgling or knocking.
- Close taps once the noise stops.
This allows trapped air to escape and restores normal operation.
6. Cleaning The Heat Exchanger
If flushing doesn’t work, the heat exchanger may need deeper cleaning. This is a job for a professional:
- The technician will disassemble the unit.
- They’ll use special tools to clean or replace the heat exchanger.
7. Correcting Installation Errors
- Check mounting hardware: Tighten or replace as needed.
- Realign pipes if they are under strain.
- Add vibration pads if missing.
If you’re unsure, ask a Navien-certified installer to review the setup.
8. Addressing Gas Supply Issues
- Check gas pressure: Low or fluctuating pressure causes noise.
- Clean burner and air intake: Remove dust or debris.
- Replace faulty gas valves if needed.
Gas repairs should always be done by a licensed professional.
9. Removing Sediment From Water Lines
- Clean the inlet water filter regularly.
- Consider installing a whole-house sediment filter if you have old pipes or well water.
This stops debris from entering the heater and causing noise.
10. When To Call A Professional
You should call a technician if:
- The noise is very loud, sudden, or new
- You smell gas or see water leaks
- DIY fixes don’t solve the problem
- The heater shows error codes
A professional can diagnose and fix complex issues safely.
How Knocking Noises Affect Your Tankless Water Heater
Ignoring a knocking noise is risky. Here’s how it can impact your heater and your home.
Reduced Efficiency
Mineral buildup or blockages make the heater work harder. This increases your energy bills and may reduce hot water output.
Damage To Heater Parts
Repeated water hammer or vibration can crack pipes, loosen connections, and damage the heat exchanger. Repairs can be costly and sometimes mean replacing the whole unit.
Shortened Heater Lifespan
A well-maintained Navien tankless heater can last 15–20 years. Knocking noises often signal problems that, if left unfixed, can cut that lifespan in half.
Water Leaks
Knocking sometimes shakes connections loose, causing leaks inside the unit or in the walls. Water damage can be expensive to repair.
Voided Warranty
If Navien finds damage due to poor maintenance or improper installation, your warranty claim may be denied. Regular checks and fixing noises early protect your investment.
Preventing Knocking Noise In Navien Tankless Water Heaters
A few smart habits can stop knocking noises before they start.
1. Regular Descaling
Flush your Navien heater every 6–12 months, especially if you have hard water. Use the manufacturer’s instructions for best results.
2. Secure Plumbing
Check pipes near the heater and throughout your home. Secure any loose sections and add insulation as needed.
3. Use Quality Installation
Hire certified professionals for installation. Make sure they use vibration pads, proper mounting hardware, and follow Navien’s guidelines.
4. Water Quality Monitoring
Install a water softener or sediment filter if your water is hard or contains debris. This reduces the risk of limescale and sediment buildup.
5. Annual Professional Inspection
Have your heater serviced once a year. A technician can catch small issues before they turn into knocking noises or bigger problems.
6. Monitor For Early Signs
Don’t ignore strange sounds. Early attention prevents costly repairs.
Comparing Knocking Noise Causes And Fixes
Here’s a quick comparison of causes and solutions for knocking noises:
| Cause | Symptoms | DIY Fix | Professional Needed? |
|---|---|---|---|
| Water hammer | Loud bang after water off | Install arrestor, secure pipes | No (unless pipes inside walls) |
| Limescale buildup | Popping, slow heat | Flush with vinegar | Yes (if severe) |
| Loose pipes | Knocking in walls | Add clamps, insulation | No |
| Faulty valve/sensor | Noise inside unit | No | Yes |
| Air in system | Gurgling, tapping | Bleed taps | No |
Signs That You Need To Replace Your Navien Tankless Water Heater
Sometimes, fixing the noise isn’t enough. Here are signs your unit may need replacement:
- Heater is over 15 years old
- Frequent repairs needed (several times a year)
- Rusty water from hot taps
- Multiple error codes that do not clear with resets
- Visible leaks or corrosion
- Loud, persistent knocking after all fixes
A new unit can save on energy and water bills, and will run more quietly.
Credit: ghurairproperties.com
Real-world Example: Fixing A Knocking Navien
Maria from Austin, TX, noticed a loud knocking from her Navien heater every time she took a shower. She checked for leaks—none. After reading her manual, she found her unit hadn’t been descaled in over two years. She bought a descaling kit, followed the instructions, and flushed the system.
The knocking stopped. As a bonus, her hot water was hotter and arrived faster. Maria now schedules descaling every spring and has had no more issues.
This shows how regular maintenance can solve and prevent knocking noise.
Costs Of Fixing Knocking Noise
How much will repairs cost? Here’s a rough guide:
| Repair/Service | Average Cost (USD) | DIY Possible? |
|---|---|---|
| Descaling | $40–$120 (kit + time) | Yes |
| Water hammer arrestor | $15–$50 each | Yes |
| Pipe insulation/clamps | $10–$30 | Yes |
| Professional inspection | $100–$200 | No |
| Part replacement (valve/sensor) | $150–$400 | No |
| Heat exchanger replacement | $500–$900 | No |
Early action keeps costs down. Delaying repairs can mean higher bills and bigger fixes later.
Credit: www.reddit.com
Myths And Mistakes About Navien Heater Knocking Noise
Many people make wrong assumptions about knocking noises. Here’s what you should know:
- Myth: All tankless heaters make noise. Fact: A quiet hum is normal, but loud knocking is not.
- Myth: Flushing the heater is optional. Fact: Skipping this can destroy your unit over time.
- Myth: Knocking is harmless. Fact: It can ruin pipes, valves, and the heater itself.
- Mistake: Using chemical cleaners not approved by Navien. These can void your warranty and damage parts.
Always follow the manual and get expert help if you’re unsure.
How Navien Tankless Water Heaters Compare To Other Brands
If you’re thinking about replacing your heater, you may wonder how Navien compares to other tankless brands for noise and reliability.
| Brand | Average Noise Level | Common Noise Issues | Maintenance Needs |
|---|---|---|---|
| Navien | Low | Knocking (if neglected) | Annual flush |
| Rinnai | Low–Medium | Clicking, water hammer | Annual flush |
| Noritz | Medium | Popping, vibration | Annual flush |
| Takagi | Medium | Rattling, popping | Annual flush |
Navien heaters are quiet if maintained properly. Most knocking issues come from skipped maintenance or plumbing problems, not design flaws.
Credit: www.callmother.com
When Knocking Noise Means An Emergency
While many knocking noises are not urgent, some need fast action:
- Loud, sudden banging that shakes the unit or pipes
- Smell of gas
- Water leaking from the heater or pipes
- Heater shutting off with error codes
In these cases, turn off your heater and water supply. Call a plumber or Navien technician right away. Waiting can mean more damage or even safety risks.
Where To Find More Help
For more details, check the official Navien website or contact their support. Plumbing forums can also help, but always use advice from trusted sources.
For further reading on tankless water heater maintenance, visit Energy.gov.
Frequently Asked Questions
Why Does My Navien Tankless Water Heater Make A Knocking Noise Only When I Shower?
This usually means water hammer or loose pipes. The sudden stop in water flow when you turn off the shower causes pipes to bang. It could also mean your heater has limescale buildup. Try securing pipes and flushing the unit.
Can Knocking Noise Damage My Navien Water Heater?
Yes. Repeated knocking can loosen connections, crack pipes, and damage internal parts like the heat exchanger. It can also shorten your heater’s life and void your warranty if not fixed.
How Often Should I Flush My Navien Tankless Water Heater?
You should flush your heater every 6–12 months. If your water is very hard, flush every 6 months. This prevents limescale and keeps the heater quiet and efficient.
Is It Safe To Use My Heater If It’s Making A Knocking Noise?
It depends on the cause. If the noise is mild and you plan to fix it soon, it’s usually safe. But if you hear loud bangs, smell gas, or see leaks, turn off the heater and call a professional.
Can I Fix Knocking Noise Myself, Or Do I Need A Professional?
You can fix simple problems like flushing the unit, securing pipes, or bleeding air. For internal parts or gas issues, always call a certified technician. DIY repairs on gas or electrical parts can be dangerous.
A Navien tankless water heater should run quietly most of the time. By understanding and fixing knocking noises early, you can keep your hot water flowing and protect your home from damage. Regular maintenance and careful attention are the keys to a long-lasting, trouble-free heater.