Flush a Water Heater
Sediment builds up at the bottom of every water heater — slowing heating, making popping sounds, and shortening tank life. A 30-minute annual flush extends the heater's life by years and improves efficiency immediately. The single best maintenance task most homeowners skip.
Tools
- ✓
- ✓For older drain valves with a square nut
- ✓For sampling the first water out
Materials
- +Older heaters have flimsy plastic valves that crack when you operate them — keep a brass replacement ($10) on hand in case
Steps
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1
Shut off heat to the tank
Gas: rotate the temperature dial to "vacation" or off. Electric: switch off the dedicated breaker at the panel. Wait 10 minutes — water doesn't need to fully cool, but the heating element shouldn't kick on during the drain.
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2
Shut off cold water supply to the tank
Find the cold water valve on top of the tank (handle on the cold/right side). Close fully.
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3
Connect hose to drain valve
At the bottom of the tank, you'll see a hose-bib-style valve. Thread on a garden hose. Run the other end to a floor drain or outside (downhill from the tank).
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4
Open a hot water tap upstairs
Open the kitchen or bathroom hot tap — this lets air into the tank so water can drain freely (otherwise it just trickles, like inverting a closed bottle).
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5
Open the drain valve
Open the drain valve slowly. Hot water flows out the hose. Let it run for 15–20 minutes — fully empty for a first flush, or until the water runs clear if you flush annually.
Tip: Catch a bucket of the first water out and look at it. If it's milky, brown, or full of grit — that's sediment and the flush is overdue. If it's clear, your annual flush has been doing its job. -
6
Flush with cold water (for heavy sediment)
With drain valve still open, briefly open the cold supply valve. Let cold water rush through, stirring up sediment, and out the drain. Repeat 2–3 times until water exiting is clear.
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7
Close drain, refill, restore heat
Close the drain valve, disconnect the hose. Fully open the cold supply valve. Leave the upstairs hot tap open — when water runs steady (not sputtering), the tank is full. Close the upstairs tap.
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8
Restore heat
Gas: relight per the directions on the heater (most are auto-relight; older are manual pilot). Electric: turn the breaker back on. Allow 30–60 minutes for full reheat.
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9
Schedule annual
Set a calendar reminder. Tank-style heaters last 8–12 years; an annually flushed tank often makes 15+. Tankless heaters get an entirely different (acid descale) treatment annually.