Tank water heaters typically last 8 to 12 years. The ones that hit 12 belong to people who flush them annually. The ones that fail at 6 belong to people who never have.
The whole reason for the gap is sediment — minerals that fall out of solution as water heats up and settle at the bottom of the tank. Sediment is bad in three ways: it insulates the burner element from the water (so the heater works harder for less hot water), it causes hot spots that corrode the tank from the inside, and it makes the heater noisy. A noisy water heater is a water heater being slowly eaten alive.
The fix is an annual flush. It takes 30 minutes, requires one tool you probably already own, and pushes the tank's death date out by years.
Here's how to do it.
What you need
- A garden hose long enough to reach a floor drain or the outside
- A flathead screwdriver
- A bucket (in case the hose connection leaks)
- 30 to 45 minutes
That's the whole tool list.
Before you start
Read this whole post before opening any valve. The flush itself is easy; the part people get wrong is the order of operations.
If your heater is gas: identify the gas control valve at the bottom front. You'll set it to pilot (or vacation, if it has one) before starting.
If your heater is electric: find the breaker for the water heater in your electrical panel. You'll flip it off before starting. Never flush an electric water heater with power on — if the elements end up exposed during the drain, they'll burn out.
If your heater is tankless: this post doesn't apply. Tankless units have their own descaling procedure (vinegar + a circulating pump), which is a different post. The HomeCanon tankless template defaults to a yearly descale and includes the procedure.
The flush, step by step
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Cut the heat source. Gas valve to pilot, or electric breaker off. Wait 10 minutes for the water inside to cool down a bit — you don't have to wait until it's room temperature, but you don't want it at 140°F either when you start handling the drain.
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Shut off the cold-water supply. The valve is on the cold-water pipe coming into the top of the heater. Turn it perpendicular to the pipe.
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Open a hot tap somewhere in the house. Pick a sink near the heater. This relieves vacuum so the tank can drain. Leave it open through the entire flush.
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Attach the garden hose to the drain valve at the bottom of the tank. Hand-tight is usually fine; don't overdo it. Route the other end to a floor drain, a utility sink, or outside.
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Open the drain valve. Most are slot-headed and need the flathead screwdriver. Water will start coming out the hose. The first few seconds will be relatively clear; then you'll see the sediment — chunks, gravel-like grit, sometimes a startling amount of rusty sludge.
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Let it drain until the water runs clear. This usually takes 5 to 15 minutes. If you've never flushed before and the heater is 4+ years old, expect 20 to 30 minutes and a lot of debris.
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Optional rinse cycle (recommended on first flush): with the drain valve still open, briefly turn the cold-water supply back on for 30 seconds. This swirls the bottom of the tank and dislodges more sediment. Turn the supply off again and let the tank drain until clear. Repeat once or twice.
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Close the drain valve. Don't overtighten — these are plastic and crack easily. Snug is fine.
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Disconnect the hose. There will be a small amount of water in it; drain it.
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Turn the cold-water supply back on. Leave the hot tap (the one you opened in step 3) running. Wait for the air to sputter out and clean, cold water to flow steadily — that's how you know the tank is full.
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Close the hot tap. Turn the heat source back on (gas valve to ON, or breaker back up).
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Wait 30 minutes for the tank to reheat. Test a hot tap. You should have hot water, possibly hotter than usual for the first cycle because the burner is no longer fighting through a layer of sediment.
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Mark it complete in HomeCanon. The next flush is queued for 12 months out.
What you might find
- Mineral grit / sand-like debris. Normal. This is calcium and magnesium carbonate that settled out.
- Rust-colored water. Some is normal; persistent heavy rust suggests the tank is corroding internally. If this is the first flush of an older tank, do a second flush in 6 months and compare. Worsening rust is a signal to start planning for replacement.
- Black flakes. Likely sacrificial anode debris (good — it's doing its job) or, if abundant, anaerobic bacteria. Both are addressed by the flush itself.
- A hissing or popping sound when reheating. Should go away after the first reheat cycle. If it persists, you have substantial sediment remaining and may need a more aggressive descale.
How often
For most homes: once a year. HomeCanon's default.
For hard-water areas: every 6 months. If your water heater is downstream of a softener, the standard yearly cadence is fine; if it's not, halve it.
For tankless: descale annually with vinegar, not a flush.
The anode rod (while you're here)
Every tank water heater has a sacrificial anode rod — a magnesium or aluminum rod that corrodes instead of the steel tank lining. Once the anode is fully consumed, the tank starts corroding. Replacing the anode every 3 to 5 years can double the tank's life.
This isn't part of the annual flush procedure — it requires draining the tank fully and unscrewing the rod from the top, which can be stubborn. If you're comfortable with that, it's a $25 part. If not, ask the plumber to swap it during your next service visit.
HomeCanon's water-heater template includes an anode-check reminder every 36 months. Tap into the schedule if you want to track it.
Why this is the easiest 30 minutes you'll spend on your house
A new tank water heater is $1,200 to $2,500 installed. Doubling its life is worth real money — and the same flush also gets you visibly hotter showers, a quieter laundry room, and a heater that's no longer making concerning noises in the night.
If you're going to do one thing on your house this month, do this.