A hot water system making noise is usually caused by sediment buildup on the heating element, water hammer in the connected pipes, a failing pressure relief valve, or thermal expansion of the tank and fittings. Each type of noise points to a different cause, and the urgency depends on the sound.
If your hot water system has started making popping, banging, hissing, or humming sounds, older systems across South Sydney are particularly prone to these faults. At Steve Bennett Plumbing, we diagnose and repair noisy hot water systems across St George and Sutherland Shire every week. This guide covers what each sound means, how urgent it is, what you can check yourself, and when you need a licensed plumber.
Why Do Hot Water Systems Make Noise?
Every hot water system produces some operational sound. A low hum during heating, a click when the thermostat cycles, or a brief gurgle during refill are all normal. The noises that signal a problem are louder, more frequent, or new sounds that were not there before.
Strange noises develop when something inside the system changes. Sediment accumulates on heating elements. Pressure builds beyond normal levels. Components loosen from years of thermal cycling. Pipes expand and contract against wall framing. Air enters the system through a fault. Each change produces a distinct sound, and that sound is the first clue to what has gone wrong.
The key question is not “is my hot water system making noise?” but “is this noise new, getting louder, or happening more often?” If the answer is yes, investigate.
What Each Noise Means and How Urgent It Is
The following noise types cover every common hot water system sound. Each one explains the cause, the urgency level, and whether you need a plumber:
Popping, Crackling, or Rumbling
This is the most common noise from storage hot water systems. It is caused by sediment buildup at the base of the tank. Minerals in the water settle and harden over time, forming a layer that traps pockets of water beneath it. When the element or burner heats the water, those trapped pockets boil and pop through the sediment layer.
Urgency: moderate. The system still works, but sediment reduces heating efficiency and shortens tank life. A professional tank flush resolves the noise and restores performance. If the sound has been present for months and is getting louder, the sediment layer is thickening and a hot water system repair should be booked soon.
Banging or Knocking
A loud bang or rapid knocking, usually when a tap is turned off, is water hammer. Water flowing through pipes at speed hits a closed valve and creates a pressure shockwave that reverberates through the pipework. This is not a fault in the hot water system itself but in the pipes connected to it.
Urgency: moderate to high. Occasional water hammer is common. Frequent or severe banging stresses pipe joints and fittings, which can cause leaks over time. A water hammer arrestor installed on the affected line absorbs the shockwave and stops the noise.
Hissing or Whistling
A hissing sound near the hot water unit usually means the pressure relief valve is releasing water. This valve is designed to open when pressure inside the tank exceeds safe limits. A constant hiss indicates excessive pressure or a faulty valve. A high-pitched whistle can also indicate restricted water flow through a partially closed valve or a clogged inlet.
Urgency: high. A pressure relief valve that discharges continuously wastes water, increases energy costs, and signals a pressure problem that can damage the tank. Do not cap or block the valve. Call a licensed plumber.
Humming or Buzzing
A low hum from an electric hot water system is often the heating element vibrating. This can happen when the element is loose, coated with scale, or nearing end of life. On heat pump systems, a hum from the compressor unit is normal during operation. A new or louder hum may indicate a failing compressor or fan motor.
Urgency: low to moderate. A slight hum during heating cycles is normal. A new, louder, or constant hum warrants inspection. Element tightening or replacement is straightforward. Compressor issues on heat pumps need specialist diagnosis.
Gurgling or Bubbling
Gurgling from the hot water system or the pipes immediately around it usually means air is trapped in the system. This can happen after a system refill, after maintenance, or when the anode rod has corroded and is releasing gas inside the tank. Gurgling from the drain near the unit may mean the pressure relief valve overflow is discharging intermittently.
Urgency: low to moderate. Air in the system after a refill usually resolves on its own within a few heating cycles. Persistent gurgling warrants inspection of the anode rod and pressure relief valve.
Ticking or Tapping
A rhythmic ticking sound is almost always thermal expansion. As the tank heats, the metal expands. As it cools, it contracts. This movement creates a ticking or tapping sound, particularly where the tank contacts wall brackets, floor stands, or pipe connections.
Urgency: low. Thermal expansion is normal. If the ticking is loud or bothersome, insulation pads between the tank and its mounting points reduce the sound. No repair is needed.
Sizzling or Steaming
A sizzling sound from a gas hot water system can indicate water dripping onto the burner or flue. On electric systems, sizzling may mean water is contacting the element through an internal leak. Steaming sounds from the pressure relief valve outlet mean the valve is discharging hot water.
Urgency: high. Internal water leaks and burner contact are both serious. Turn off the power or gas supply to the unit and call a licensed plumber immediately. For urgent situations, contact our emergency plumbing service.
Quick Diagnostic: Is This Noise Dangerous?
Not all noises are emergencies. Use this diagnostic to determine your next step:
| Sound | Most Likely Cause | Urgency | Action |
| Popping or rumbling | Sediment buildup | Moderate | Book a tank flush |
| Banging or knocking | Water hammer | Moderate | Install arrestor |
| Hissing or whistling | Pressure relief valve or restriction | High | Call plumber |
| Humming or buzzing | Element vibration or compressor | Low to moderate | Monitor, then inspect |
| Gurgling or bubbling | Air in system or anode rod | Low to moderate | Monitor, then inspect |
| Ticking or tapping | Thermal expansion | Low | No action needed |
| Sizzling or steaming | Internal leak or burner contact | High | Turn off supply, call plumber |
More: Water Hammer in Pipes: What It Means and How to Stop It
Noises Specific to Each Hot Water System Type
Different systems produce different noises for different reasons. Here is what to listen for on each type:
Gas Storage Systems
Gas storage systems produce a soft whoosh when the burner ignites and a low rumble during heating. Abnormal noises include loud popping (sediment on the heat exchanger), delayed ignition bangs (dirty burner or thermocouple issue), and hissing from the pressure relief valve. A gas system that bangs loudly on ignition needs immediate attention because delayed ignition can damage the burner chamber.
Electric Storage Systems
Electric systems are quieter than gas during normal operation. The main noises are popping from sediment on the element, humming from element vibration, and ticking from thermal expansion. Systems on off-peak (controlled load) tariffs heat overnight, so homeowners may hear these sounds in the early hours. This is normal timing, but new or louder sounds during the heating cycle still warrant investigation.
Continuous Flow (Tankless) Systems
Continuous flow systems produce a click and a brief flame sound when the burner fires on demand. Abnormal noises include a loud bang at ignition (gas valve or burner issue), high-pitched whining (fan motor bearing), and vibrating or rattling (loose internal components or heat exchanger scaling). These systems have error codes on the display that often correspond to the noise source.
Heat Pump Systems
Heat pumps produce a constant low hum from the compressor and fan during operation. This is normal. Abnormal noises include grinding (failing compressor), rattling (loose fan blade or mounting bolts), clicking (faulty relay or control board), and loud vibration (compressor mounting failure). Heat pump noise issues are often related to the outdoor unit and can be affected by proximity to walls or fences that reflect sound.
What to Do Before Calling a Plumber
A few safe checks can help you identify the source and urgency before booking a service call:
Identify the Exact Source
Stand near the hot water system and listen carefully. Determine whether the noise is coming from the unit itself, the pipes connected to it, or the wall behind it. This narrows the cause and helps the plumber diagnose the issue faster.
Check the Pressure Relief Valve
Look for a small copper pipe running from the valve on the side of the tank to a drain or outside the building. If water is dripping or flowing from this pipe, the pressure relief valve is discharging. This is a high-urgency sign that needs professional attention.
Listen During a Heating Cycle
Run a hot tap to draw hot water from the tank, then close it and wait for the system to reheat. Listen for the noise during the refill and heating cycle. Noises that only occur during heating point to sediment or element issues. Noises that occur when taps close point to water hammer.
Check the Age of the System
Storage hot water systems typically last 8 to 12 years. Continuous flow systems last 15 to 20 years. If your system is at or beyond these ages, new noises often signal components reaching end of life. A plumber can advise whether repair or replacement is more cost-effective.
Do Not Ignore New Sounds
A new noise that was not there last month is always worth investigating. Hot water system faults tend to worsen gradually. A popping sound today can become a failed element next month. A hissing valve today can become a burst tank fitting next quarter. Early diagnosis saves money.
When to Call a Licensed Plumber
Call a plumber if you hear sizzling, steaming, or hissing from the unit, if the pressure relief valve is continuously discharging, if the noise is getting louder over time, if banging occurs frequently and is severe, or if the system is older than 10 years and making any new sounds. All hot water system repairs in NSW must be carried out by a licensed plumber. You can verify any plumber’s licence through Service NSW before booking.
Why Noisy Hot Water Systems Are Common in South Sydney
The housing stock and system age across St George and Sutherland Shire make hot water system noises more frequent:
Ageing Electric Storage Systems on Off-Peak Tariffs
Homes across Hurstville, Kogarah, and Peakhurst have a high proportion of electric storage systems on controlled load tariffs. These systems heat overnight, and sediment-related popping during the early hours is one of our most common callout triggers. Many of these units are 10 to 15 years old with heavy sediment buildup that has never been flushed.
Gas Systems in Post-War Housing
Mortdale, Oatley, and Carlton have many homes with older gas storage systems where burner assemblies and thermocouples have not been serviced in years. Delayed ignition bangs on these units are a clear sign of overdue maintenance.
Coastal Corrosion Accelerating Component Failure
Cronulla, Caringbah, and Sans Souci face salt-heavy air that corrodes pressure relief valves, anode rods, and external fittings faster than inland suburbs. A hissing pressure relief valve in a coastal home is often a corrosion-driven failure that needs replacement rather than adjustment.
Heat Pump Installations in Newer Renovations
Miranda, Sylvania, and Kirrawee have seen a rise in heat pump installations over the past 5 years. Homeowners unfamiliar with heat pump operation sometimes report normal compressor hum as a fault. Understanding what is normal for your system type prevents unnecessary callouts.
Water Hammer in Homes With Mixed-Age Plumbing
Menai and Engadine have properties where bathrooms and kitchens were renovated at different times, creating pipe diameter mismatches and unsupported pipe runs. These conditions amplify water hammer when hot taps are closed quickly, producing loud banging that sounds like it is coming from the hot water system itself.
How a Licensed Plumber Diagnoses and Fixes a Noisy Hot Water System
When the noise needs professional attention, here is what to expect:
System Inspection and Sound Identification
A licensed plumber starts by listening to the system under operating conditions. They identify the sound type, source location, and timing (during heating, during draw-off, or at rest). This narrows the likely cause before any disassembly.
Tank Flush and Element Inspection
For sediment-related noises, the tank is drained and flushed to remove accumulated deposits. The heating element is inspected for scale buildup and wear. The anode rod is checked and replaced if depleted. This is the most common fix for popping, rumbling, and crackling noises.
Pressure Relief Valve Test and Replacement
The pressure relief valve is tested by briefly lifting the lever to confirm it opens and closes cleanly. If it drips continuously, it is replaced. The plumber also checks the system pressure with a gauge. If pressure exceeds the safe range, a pressure-limiting valve may be recommended. Steve Bennett Plumbing diagnoses pressure-related noises as part of every hot water service call.
Water Hammer Arrestor Installation
For banging caused by water hammer, a hammer arrestor is installed on the affected pipe line. This small device absorbs the pressure shockwave and eliminates the banging. The plumber also checks pipe brackets and mounting clips to ensure pipes are properly secured.
Gas Burner and Ignition Service
For gas systems with delayed ignition bangs, the burner assembly, thermocouple, and gas valve are cleaned, tested, and adjusted. A gas system that bangs on ignition is a safety concern and should be serviced promptly. All gas work must be carried out by a licensed gas fitter. You can learn more about our team and 40-year history of hot water and gas fitting services across South Sydney.
After installing a new hot water system for a homeowner in our service area, Steve Bennett Plumbing received this feedback: “Steve Bennett Plumbing were easy to deal with and very prompt. Well priced and transparent. Thanks for a quick turnaround with our hot new water system.” Adem Mich. That transparency and speed is what every hot water job should deliver.
More: The Complete Guide to Hot Water Heaters for Your Home
How to Prevent Hot Water System Noises
Regular maintenance prevents most noises before they start:
Flush the Tank Every 3 to 5 Years
A professional tank flush removes sediment before it hardens into the thick layer that causes popping and rumbling. This is the single most effective noise prevention measure for storage systems. Steve Bennett Plumbing offers scheduled plumbing maintenance visits that include tank flushing.
Replace the Anode Rod on Schedule
The anode rod protects the inside of the tank from corrosion. Once it is fully depleted, the tank itself starts corroding, which produces gurgling, crackling, and eventually leaks. Have the anode rod inspected every 3 to 5 years and replaced when needed.
Install a Pressure-Limiting Valve
If your household water pressure exceeds 500 kPa, a pressure-limiting valve protects the hot water system and all connected fixtures. High pressure accelerates wear on the pressure relief valve and contributes to hissing and whistling noises. Choose WELS-rated water-efficient fixtures when upgrading taps and showerheads to reduce stress on the system.
Secure Loose Pipes
Check exposed hot water pipes for loose brackets or clips. Tighten or replace any that have come loose. Properly secured pipes reduce thermal expansion ticking and water hammer banging.
Know Your System’s Age and Service History
Write down the installation date and keep a record of every service. When the system passes 10 years (storage) or 15 years (continuous flow), increase the frequency of inspections. A noisy older system is often the first warning before a major failure. Book a hot water system installation consultation if replacement is approaching.
More: Why Do I Have No Hot Water? Common Causes and What to Do
Areas We Service
Steve Bennett Plumbing serves homeowners across the St George and Sutherland Shire regions. Our service area includes Hurstville, Kogarah, Peakhurst, Sans Souci, Mortdale, Oatley, Carlton, Miranda, Cronulla, Engadine, Caringbah, Kirrawee, Sylvania, Menai, and Gymea.
Stop Your Hot Water System Noise Before It Gets Worse
If your hot water system has started making sounds it did not make before, do not wait for it to fail. Strange noises are your system’s early warning. A 30-minute diagnostic visit now prevents a midnight breakdown that leaves you without hot water.
Call Steve Bennett Plumbing today on 02 9538 7864 or reach our emergency line on 0413 158 600.
With over 40 years of hot water expertise across St George and Sutherland Shire, we service, repair, and replace every system type: gas storage, electric storage, continuous flow, solar, and heat pump. Every callout includes a $0 call-out fee, fixed-price quote, and same-day service where possible. Our lifetime labour warranty means the repair stays quiet. We respond to emergencies when a hissing valve or sizzling element needs urgent attention.
Frequently Asked Questions
Why is my hot water system making noise?
The most common causes are sediment buildup on the heating element (popping or rumbling), water hammer in connected pipes (banging), a failing pressure relief valve (hissing), or thermal expansion (ticking). The type of sound tells you the cause and how urgent it is.
Is a noisy hot water system dangerous?
Most noises are not immediately dangerous. However, hissing from the pressure relief valve, sizzling from an internal leak, and loud bangs from delayed gas ignition are high-urgency sounds that need prompt professional attention. Ignoring these can lead to system failure or safety hazards.
Why is my hot water system making a knocking noise?
Knocking or banging is almost always water hammer. It occurs when water flowing through the pipes hits a closed valve and creates a pressure shockwave. A water hammer arrestor installed on the affected line eliminates the sound and protects pipe joints from stress damage.
Why is my gas hot water system making noise?
Gas systems commonly produce popping (sediment on the heat exchanger), a whoosh on ignition (normal), a loud bang on ignition (delayed ignition from a dirty burner), or hissing from the pressure relief valve. A loud ignition bang is a safety concern that needs servicing.
Do hot water systems normally make noise?
Yes. A low hum during heating, a click from the thermostat, a brief gurgle during refill, and a soft whoosh from a gas burner ignition are all normal operational sounds. Investigate any noise that is new, louder than usual, or increasing in frequency.
When should I call a plumber about a noisy hot water system?
Call a licensed plumber if you hear sizzling or steaming, if the pressure relief valve is dripping continuously, if you hear loud bangs from a gas system on ignition, if noises are getting progressively louder, or if your system is older than 10 years and making any new sounds.
