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Szeto Plumbing · San Gabriel Valley

How to flush a tank water heater

Flushing a tank water heater clears the mineral sediment that SGV's hard water leaves behind.

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Mon–Sat 8:30 AM–7 PM · San Gabriel Valley

Mon–Sat, 8:30 AM–7 PM

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Kitchens, baths, heaters, main lines

Updated · 3 min read

Short answer

Turn the gas control to pilot (or switch off power), close the cold supply, attach a hose to the drain valve, open a hot tap, and drain. Then open the cold supply in short bursts until the water runs clear, close the drain, refill, and relight.

On this page
  1. Why flushing matters in the SGV
  2. Draining
  3. Flushing out sediment
  4. When to call instead
  5. Common questions

Why flushing matters in the SGV

Water across the western San Gabriel Valley ranges from moderately hard to very hard. Monterey Park's city wells average 220 mg/L and Alhambra reports about 240 ppm.

Those minerals settle on the tank bottom. Flushing them out keeps heating efficient and quiets popping sounds.

Gas to pilot or power off then Close cold supply then Hose on drain valve then Open a hot tap then Drain the tank1Gas to pilot or power off2Close cold supply3Hose on drain valve4Open a hot tap5Drain the tank
Getting the tank ready to drain.

Draining

Run the hose outside or to a floor drain that can take hot water. Open the drain valve slowly.

Opening a hot tap upstairs or nearby lets air in so the tank drains faster.

Flushing out sediment

Once the flow slows, open the cold supply for a few seconds at a time. The rush stirs sediment off the bottom and out the drain.

Repeat until the water at the hose runs clear. Then close the drain valve and leave the cold supply open to refill.

Burst of cold water then Watch for clear water then Close drain valve then Refill with tap open then Relight or power on1Burst of cold water2Watch for clear water3Close drain valve4Refill with tap open5Relight or power on
Finishing the flush and bringing the heater back.

When to call instead

Old plastic drain valves on long-neglected tanks can clog with sediment and leak when opened. Swapping in a full-port brass valve solves that.

Common questions

Should I fill the tank before relighting?

Yes. Fill until water flows steadily from the open hot tap, then relight or restore power. An electric element can burn out if powered dry.

How often should I flush?

At least yearly per many maker manuals, and more often in very hard water.

Can flushing fix a leaking tank?

No. Flushing removes sediment but cannot repair rusted steel.

Sources