Why Is My Tankless Water Heater Making Noise?
A tankless water heater may make noise due to mineral buildup, high water pressure, or loose components inside the unit. Regular flushing and maintenance usually prevent these issues and help the system operate quietly.
Tankless water heaters are usually very quiet. If your system begins making unusual noises such as rumbling, rattling, or high-pitched sounds, it may indicate a maintenance issue or a minor problem inside the unit.
In most cases, these noises are caused by mineral buildup, water pressure issues, or loose components. Fortunately, many of these problems can be diagnosed and corrected with basic troubleshooting.
This guide explains the most common reasons a tankless water heater makes noise and how to fix them.
Common Noises from Tankless Water Heaters
Different sounds may point to different causes. Some of the most common noises homeowners report include:
• rumbling or vibrating
• high-pitched whining
• clicking or tapping sounds
• rattling or humming
Understanding the type of noise helps identify the underlying issue.
Why Tankless Water Heaters Sometimes Vibrate
Some homeowners notice a vibrating or humming sound coming from the unit or nearby pipes. This usually happens when water pressure fluctuates or when pipes are not securely mounted.
Vibration may occur if:
• water pressure is too high
• mounting brackets are loose
• pipes are touching walls or framing
• the unit is mounted on a thin wall
In many cases, tightening mounting hardware or adding pipe insulation can reduce vibration.
If the sound seems to come directly from the heater, a technician may need to inspect the internal fan or motor components.
Mineral Buildup in the Heat Exchanger
The most common cause of tankless water heater noise is mineral scale buildup inside the heat exchanger.
When hard water minerals accumulate, water flow becomes restricted. As heated water moves through these deposits, it can create rumbling or vibrating sounds.
Over time, scale buildup may also reduce efficiency and strain internal components.
Regular tankless water heater maintenance helps prevent this issue and keeps the heater operating quietly.
👉 See our guide on tankless water heater maintenance for recommended servicing practices.
System Needs Flushing
If mineral buildup becomes significant, the system may require flushing to remove the scale.
Flushing circulates a cleaning solution through the heat exchanger to dissolve mineral deposits and restore proper water flow.
👉 See our step-by-step guide on how to flush a tankless water heater to remove mineral buildup.
Routine flushing is one of the most important maintenance tasks for tankless systems.
High Water Pressure
Excessively high water pressure can also cause unusual sounds inside a tankless water heater.
When water pressure exceeds recommended levels, it may produce:
• vibrating pipes
• humming sounds
• rattling valves
Most homes operate best with water pressure between 40–60 PSI. If pressure is too high, installing a pressure regulator may help resolve the issue.
Sediment Buildup in the Water Lines
In addition to mineral scale inside the heat exchanger, sediment can sometimes accumulate in water lines connected to the heater.
Small particles may restrict water flow and create unusual sounds as water moves through the system.
Symptoms of sediment buildup may include:
• rattling sounds inside pipes
• reduced hot water pressure
• inconsistent water temperature
Cleaning the inlet water filter and flushing the system periodically can help prevent sediment from causing noise issues.
Loose Internal Components
Some noises may be caused by loose components inside the unit or mounting hardware.
Over time, vibration from normal operation can cause small parts to shift slightly.
A technician may inspect:
• fan components
• mounting brackets
• internal fasteners
Tightening loose components can often eliminate rattling noises.
Venting Issues
Tankless gas heaters rely on proper airflow for combustion.
Blocked or damaged vent pipes can sometimes cause unusual noises or vibrations.
Check for:
• debris blocking outdoor vent openings
• damaged vent pipes
• loose vent connections
Proper venting ensures safe and efficient operation.
How to Check for Simple Causes of Tankless Heater Noise
Before calling a technician, homeowners can check a few simple things.
Start by inspecting the surrounding plumbing and connections.
Basic checks include:
- Ensure the unit is securely mounted to the wall.
- Check that water pipes are properly supported.
- Inspect vent pipes for loose connections.
- Verify that water pressure is within normal range.
If these basic checks do not resolve the issue, the noise may originate from internal components that require professional inspection.
When to Call a Professional
If unusual sounds continue after basic troubleshooting, it may be best to have a professional inspect the system.
A technician can diagnose issues such as:
• worn fan motors
• failing internal components
• combustion problems
• electrical faults
Professional servicing helps ensure the system operates safely.
Preventing Tankless Water Heater Noise
The best way to prevent noise problems is through regular maintenance.
Preventative steps include:
• annual system flushing
• cleaning the water inlet filter
• inspecting venting systems
• monitoring water pressure levels
These simple maintenance tasks help keep your tankless heater running efficiently and quietly.
Related Tankless Water Heater Troubleshooting
Unusual noises may sometimes appear alongside other symptoms such as inconsistent temperatures or reduced water pressure.
For more common issues, see our tankless water heater troubleshooting guide.
Is Tankless Water Heater Noise Dangerous?
Most tankless heater noises are not dangerous, but they should still be investigated.
Minor noises may simply indicate routine maintenance is needed. However, persistent sounds could signal issues that affect efficiency or long-term performance.
If the heater produces loud knocking, grinding, or buzzing sounds, it is best to have the system inspected to ensure safe operation.
Regular maintenance helps prevent most noise-related problems.
Frequently Asked Questions
Is it normal for a tankless water heater to make noise?
Tankless heaters usually operate quietly. Occasional clicking or fan sounds are normal, but loud rumbling or vibrating noises may indicate mineral buildup or maintenance issues.
Can flushing stop tankless heater noise?
Yes. If mineral scale buildup is causing the noise, flushing the system can often restore normal operation.
How often should tankless heaters be flushed?
Most manufacturers recommend flushing the system once per year, or more frequently in homes with hard water.