Why Is My Hot Water Heater Making Noise When the Water Is Off?

If your hot water heater is making noise when the water is off, start by listening closely and noting when it happens. The most common culprits are harmless pipe expansion clicks, sediment rumbling in a storage tank, or a relief valve briefly hissing as the system heats. Below is a practical way to identify the sound, fix the easy stuff, and spot the red flags that mean you should call a licensed plumber.

Quick answer: what the noise probably is

Match the sound you hear to the likely cause:

• Ticking/creaking from walls or near the tank: Hot copper pipes expanding and rubbing against timber or clips. Annoying but common after showers or a reheat cycle.
• Rumbling, popping or kettle-like sounds from a storage tank: Sediment on the base or electric elements causing water to superheat and release steam bubbles. Often worse on off-peak overnight reheats.
• Short hiss or gurgle at a valve with a drain line: Your TPR (temperature and pressure relief) valve or, in some homes, an ECV (expansion control valve) venting during a heat cycle. Brief activity is normal.
• Continuous hissing or a steady trickle from the TPR drain: Not normal. Could indicate overpressure, a failed valve, or overheating. Turn the system off and call a plumber.
• Single bang when another tap or appliance shuts: Water hammer. Fit hammer arrestors and secure pipework.
• Fan or compressor cycling on a unit outside: Heat pump or continuous-flow unit doing a scheduled run, defrost or post-purge. Usually normal; timing and mounting can reduce disturbance.
• Gurgling on very hot afternoons (solar hot water): Collector loop expanding or stagnating. Occasional noise can be normal, but get solar circuits serviced if frequent or accompanied by leaks.

Safety first: when to turn it off and call a pro

Hot-water systems store energy under pressure. If you notice any of the following, act promptly:

• Continuous discharge of hot water or steam from the TPR drain line (not just a brief dribble while heating). Turn off power/gas and the cold-water supply to the unit and call a licensed plumber.
• Very hot water at taps (scalding) or the cylinder feels excessively hot to touch on the outer jacket — possible thermostat/controls fault. Isolate and call a plumber/electrician.
• Strong gas smell near a gas unit. Turn off the gas isolation valve if safe and contact your gas distributor’s emergency line.
• Loud, repeated bangs or boiling/tea-kettle sounds that don’t subside. Isolate and get it inspected.
• Burn marks, melted plastic, or scorch marks on or around the unit. Isolate power/gas and call a pro.

Troubleshooting checklist (most likely causes first)

1. Identify your system type.

   Look for: a big cylinder (storage), a rectangular box on the wall (continuous flow), a tall cylinder with a fan/compressor on top or beside it (heat pump), panels on the roof (solar). Knowing this narrows the noise sources.

2. Locate the sound.

   Stand near the tank or unit. Is the noise from the TPR valve (the one with a test lever and drain line), the cold inlet valve/ECV (often also with a drain line in NSW/QLD), the cylinder body, or pipework in a wall/ceiling?

3. Decide if valve venting is normal or not.

   During a heat cycle, brief hissing and a warm dribble from the TPR or ECV is expected as water expands. Not normal: a continuous stream, very hot water discharging, or noise that continues long after heating stops. That points to a failed valve, excessive pressure or a control fault — call a plumber.

4. Pipe expansion clicks/ticks?

   Open the cupboard or area where hot pipes run. If ticking stops when you gently press on the pipe, it’s expansion. Fixes include adding/adjusting pipe clips with cushioning, insulating hot lines near the unit, and giving pipes clearance where they pass through studs. A plumber can also re-route tight bends that bind.

5. Rumbling or popping from a storage tank?

   That’s usually sediment on the base or around an electric element. Flushing helps:

   1. Turn off power at the switchboard (HWS) or turn the gas control to pilot/off.
   2. Close the cold-water isolation valve to the heater.
   3. Attach a hose to the drain valve, run it to a safe drain, and open the valve.
   4. Lift the TPR lever briefly to let air in so it drains. When the water runs clear, close the drain, close the TPR, reopen the cold supply and bleed air from a hot tap.
   5. Restore power/gas once the tank is full and air-free.

   If noise returns quickly, book a service. A plumber can do a deeper flush, check the anode (often 3–5 year intervals in harder water) and replace scaled elements.

6. Water hammer thuds when other taps shut?

   High pressure or fast-closing mixers/washing machines can bang pipes even with the hot tap off. Fixes: secure any loose pipes, have a plumber fit mini hammer arrestors at problem fixtures, and check/fit a pressure limiting valve at the meter or on the hot inlet.

7. Heat pump or continuous-flow fan noise?

   These can run briefly with no taps open for defrost, sanitisation or a post-burner purge. To reduce disturbance: schedule heating to daytime if you’re on off-peak (see our guide to off-peak hot water), sit the unit on rubber feet, clear leaves from the fan, and service annually. Abnormal sounds (grinding, squeal) need a technician.

8. Chattering valves (tempering or pressure valves)?

   A vibrating or buzzing near the tempering valve or a pressure-reducing valve points to wear, debris or high pressure. Replacement is the cure; ask the plumber to test your incoming pressure while they’re there.

9. Solar thermal gurgles on hot days?

   Occasional gurgling in the collector loop can be normal expansion. If frequent, noisy or accompanied by relief valve discharge, book a solar hot water service to check glycol (if used), air in the loop, and the solar-rated relief valves.

10. Controls and temperature settings.

    Storage tanks in Australia should store at 60 °C for Legionella control, then a tempering valve blends down to safe tap temperatures. Don’t lower a hidden thermostat. If your system has a user controller, keep storage at 60 °C and adjust only the tempering or outlet setting. If water is scalding or you hear boiling, isolate and call a pro.

Fixes that actually quieten hot-water noise

• Secure and cushion hot pipes: Add/adjust clips, sleeve pipes where they pass through studs, and insulate the first few metres of hot line from the tank.
• Flush the tank annually if you’re in a sediment-prone area. It reduces rumbling and improves efficiency.
• Replace tired valves: TPRs, ECVs, tempering and pressure-reducing valves wear out. Swapping them restores quiet operation and safety.
• Fit hammer arrestors at noisy fixtures and check mains pressure. A plumber can measure static and dynamic pressure and recommend a pressure limiting valve if needed.
• Service heat pumps/continuous-flow units: Clean filters (if applicable), clear airflow, tighten mounts, and update timers to avoid night-time cycles.
• Consider an expansion vessel on the hot side where local practice allows and if your ECV vents excessively. Your plumber will advise based on your state’s requirements and water authority rules.

Preventive maintenance (Australia-specific)

• Exercise the TPR valve as per the manufacturer’s instructions (often every 6 months) to clear scale. Stand clear; hot water may discharge from the drain line.
• Check the anode on glass-lined cylinders every 3–5 years (more often in hard/bores). Replacing it can extend tank life and reduce rumbling.
• Keep clearances around outdoor units and cylinders so valves and drains are accessible and audible issues aren’t hidden.
• Off-peak timing: If night-time rumbling wakes you, talk to your electrician/plumber about reheating earlier in the evening or spreading cycles. See our guide to off-peak hot water.
• Annual service: A licensed plumber can test safety valves, check combustion/controls, and catch small issues before they become noisy (or dangerous) problems.

What if the noise only happens once the water is off?

That’s the tell-tale pattern for thermal expansion. When taps are shut, water in the system is trapped; as the tank heats, pipes and water expand and valves may vent briefly. A little ticking or a short hiss is expected. Continuous discharge, very loud bangs, or boiling noises are not — shut it down and book a service.

Bottom line: a hot water heater making noise when water is off is usually a minor expansion or sediment issue you can tame with simple maintenance. Keep an ear out for the danger signs, and don’t hesitate to involve a licensed plumber if anything seems off.