Water Heater Making Noise? Here's What Each Sound Means

A water heater should run quietly. When it starts making noise, it is telling you something — and different sounds indicate different problems with different urgency levels. Here is a diagnostic guide to water heater sounds.

Popping or Rumbling

What it means: Sediment buildup on the tank bottom. This is the most common water heater noise and is caused by a layer of mineral scale that has accumulated from hard water. As the burner heats the water, it must push through this layer, creating steam pockets that collapse with a characteristic popping or rumbling sound.

Urgency: Medium. This is a sign that the unit has not been maintained and is working harder than it should. Annual flushing from the point of installation prevents this. If the sounds are minor, flushing may resolve them. If the sounds are severe — loud banging rather than soft rumbling — the sediment layer may be thick enough to cause damage, and the unit is likely approaching end of life.

Hissing

What it means: Most commonly, water contacting a hot surface — either a small leak dripping onto the burner, condensation dripping on a hot surface, or the T&P valve briefly opening due to overpressure.

Urgency: High if accompanied by burning smell or gas smell — investigate immediately. Medium if it happens only during the heating cycle without other symptoms (may be normal condensation on a new unit in the first few weeks).

Screeching or Whining

What it means: Usually a partially closed valve — either the cold water inlet valve or the shut-off valve — that is restricting water flow and creating a high-pitched sound as water forces through the partial restriction.

Urgency: Low. Open the relevant valves fully and the sound should stop immediately. If it persists with all valves fully open, have a plumber inspect the unit.

Ticking or Tapping

What it means: Often normal. Heat trap fittings — components that prevent convective heat loss through the inlet and outlet pipes — contain small check valves that tick as they open and close with water flow. This is normal and harmless.

Urgency: None if it occurs only during and just after water draw. If ticking is constant or very loud, check for a loose connection.

Knocking or Banging (Pipes)

What it means: "Water hammer" — a phenomenon where rapid water flow is suddenly stopped, creating a pressure wave that travels back through the pipes and makes a knocking or banging sound. Often triggered by fast-closing solenoid valves in dishwashers and washing machines.

Urgency: Low for the water heater itself, but water hammer can damage pipes and fittings over time. A water hammer arrestor installed on the affected supply line resolves this permanently.