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A water heater that pops and rumbles

Popping or rumbling from a tank water heater usually means mineral sediment on the tank bottom.

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Updated · 3 min read

Bottom line

Popping is steam bubbles escaping through a layer of mineral sediment on the tank bottom. Flushing the tank removes loose sediment and quiets it; a tank that keeps rumbling after flushing has hardened scale and is nearing the end of its life.

Contents
  1. Where the sound comes from
  2. Why Monterey Park tanks get loud
  3. What sediment costs you
  4. Flushing and when it is too late
  5. Before you call

Where the sound comes from

On a gas heater, the burner heats the tank bottom. When sediment covers it, water trapped under the layer flashes to steam and bursts through.

That is the pop. Rumbling is many of those bursts at once, and it means the layer is thick.

Hard water heated then Minerals settle then Layer covers tank bottom then Trapped water boils then Popping and rumbling1Hard water heated2Minerals settle3Layer covers tank bottom4Trapped water boils5Popping and rumbling
What causes water heater noise.

Why Monterey Park tanks get loud

City well water averages 220 mg/L hardness, according to the 2025 water quality report. That is very hard water, and much of the mineral content settles as the water heats.

Tanks here collect sediment faster than in soft-water cities. Noise can start within a few years if the tank is never flushed.

What sediment costs you

  • Less efficient heating, because heat has to pass through the layer
  • Overheating of the tank bottom, which stresses the glass lining
  • Clogged drain valves that will not close fully
  • Less hot water than the tank's rated size

Flushing and when it is too late

A flush shuts off the burner, drains the tank through a hose, and runs cold water through until the discharge clears. Sediment that has hardened into scale may not come out.

Flush helps: Noise drops after draining; Water runs clear; Valve closes tight. Near end of life: Noise returns quickly; Rust in hot water; Water at the baseFlush helps• Noise drops after draining• Water runs clear• Valve closes tightNear end of life• Noise returns quickly• Rust in hot water• Water at the base
Telling a tank that needs flushing from one that needs replacing.

Old drain valves on heaters that have never been opened sometimes leak after a flush. Replacing the drain valve with a full-port brass one is a common add-on.

Before you call

Is a popping water heater dangerous?

It is usually not dangerous by itself, but it signals strain on the tank. Check that the relief valve works.

Do electric water heaters make the same noise?

They can hiss or crackle when sediment buries the lower element, which can also burn the element out.

How often should a tank be flushed here?

Very hard water calls for more frequent flushing than the yearly minimum many makers suggest.

Cited sources