Strange Noises from Water Heater
Updated February 20, 2026
Popping, rumbling, crackling, hissing? Almost always sediment buildup. Water trapped under the layer superheats and steam bubbles pop as they escape. Warning sign that the heater is overworked and maintenance is overdue.
Overview
Different sounds, different problems. Popping and rumbling: water trapped under sediment turns to steam. Thicker the layer, louder the noise. Crackling on electric: scale on the elements. Hissing when gas burner fires: condensation (usually normal). Whining when hot water flows: restricted valve. Flushing resolves most cases. If noise persists after flushing, sediment has hardened or the tank is nearing end of life.
Symptoms
- Popping or knocking during heating cycles -- sounds like water starting to boil. Most common noise.
- Low rumbling for several minutes each cycle -- thick sediment layer, multiple steam pockets
- Crackling or sizzling on electric heater -- scale encrusting the lower element
- Hissing when gas burner fires -- condensation dripping onto the burner. Common, usually not a concern.
- High-pitched whine when hot water runs -- flow restriction: partially closed valve, kinked line, or clogged heat trap nipple
- Ticking from nearby pipes -- thermal expansion. Pipes expand and contract against straps or framing.
Common Causes
- Sediment on the tank bottom -- minerals precipitate and settle. Insulating layer traps water that superheats and pops. Classic popping and rumbling.
- Scale on electric elements -- limescale encrusts the lower element. Heats hotter to compensate, water percolates through the scale. Crackling and sizzling. Reduces efficiency and shortens element life.
- Condensation on gas burner -- cold water enters, condensation forms and drips onto the burner. Normal, especially first cycle or cold weather.
- Thermal expansion in pipes -- copper or PEX expands slightly. Tight holes or rigid straps create ticking. Harmless pipe issue, not the heater.
- End of life -- flushing no longer resolves the noise. Sediment has hardened into calcite that cannot be flushed. Heater working harder, higher energy costs, accelerated corrosion. 8+ years with persistent noise means plan replacement.
What You'll Need
How to Fix It
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Identify the Type of Noise
Popping/rumbling during heating: sediment. Crackling on electric: element scale. Hiss when gas fires: condensation (normal). Whine when hot water flows: restricted valve. Ticking from pipes: thermal expansion. Match the sound to the fix.
Tip: Hand on the side of the tank while listening. Feel vibration with the popping? Definitely sediment. Steam bubbles collapsing inside. -
Flush the Water Heater Tank
Power off, cold supply off. Garden hose on the drain valve to a floor drain or outside. Drain completely -- sediment particles and discolored water. Open cold supply briefly to stir and flush remaining sediment. Repeat until clear. Close, refill, restore power. Noises should be significantly reduced or gone.
Warning: Water is hot. Cool for hours or handle the discharge carefully. Drain valve clogs with sediment? Wire to break the blockage, or have a plumber replace with a full-port ball valve. -
Descale Electric Heating Elements
Electric heater crackling? Lower element has scale. Breaker off, drain below element level. Element wrench (1-1/2 inch socket) to remove. Thick white/gray scale? Soak in vinegar 2-4 hours or replace ($10-25). Wet-dry vacuum through the element opening to suction sediment. Reinstall, refill, power on.
Tip: Low-watt-density elements heat slower but produce less scale. If scale recurs, switch to low-watt-density at next replacement. -
Address Thermal Expansion Noise in Pipes
Ticking from pipes? Thermal expansion. Not harmful but annoying. Give pipes room to move: enlarge tight holes through framing, foam insulation at pass-through points. Replace rigid copper straps with padded or plastic. Expansion tank reduces stress on the system.
Tip: CPVC pipes tick more than copper -- higher expansion rate. Same fixes: insulate pass-throughs, flexible supports. -
Address Flow Restriction Noises
Whine only when hot water runs? Flow restriction. Shutoff valves fully open? Heat trap nipples (brass fittings with internal check balls) can rattle or whine if the ball sticks. Remove and clean, or replace with standard dielectric nipples.
Tip: Whining from specific faucets, not the heater area? Worn cartridge or clogged aerator. Run hot at different fixtures to isolate. -
Evaluate for Replacement (If Flushing Does Not Help)
Flushed but noise returns within weeks? Sediment has hardened into calcite that cannot be flushed. Permanent insulator, dramatically reduced efficiency, accelerated corrosion. Over 8-10 years old and flushing does not help? Plan replacement.
Tip: Compare first-hour rating, not just tank size. High-efficiency 40-gallon can outperform a standard 50 in hot water delivery.
When to Call a Pro
Call a plumber if the drain valve is clogged and will not open, if noise persists after flushing and you want a tank assessment, if electric elements need replacing and you are not comfortable with electrical, if the sound is loud banging (not popping -- could be hammer or something serious), or if it is over 10 years old with persistent noise.
Prevention Tips
- Flush annually. Single most effective way to prevent sediment noise and maintain efficiency.
- Water softener for hard water (above 7 GPG). Dramatically reduces sediment and scale.
- Anode rod every 3-5 years. Prevents corrosion that adds rust to the sediment layer.
- Thermostat at 120. Lower temperatures slow mineral precipitation.
- Electric heater? Low-watt-density elements produce less scale and run quieter.
- Expansion tank if your system has a check valve or PRV. Prevents pressure-related noise and protects the tank.