How often should you flush your water heater?
Updated July 2026
Flush a tank water heater once a year — and every 6 months if you're in a hard-water area (much of the Southwest, Midwest, and Florida). Tankless units need an annual vinegar or descaler flush instead. The point is sediment: dissolved minerals settle out of heated water and build a layer on the tank bottom that insulates the burner from the water, wastes energy, and shortens the tank's 8–12-year life.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Soft or softened water | Every 12 months | A working softener removes most of the minerals that become sediment |
| Moderately hard water (3–7 grains) | Every 12 months | The standard manufacturer recommendation |
| Hard water, no softener (7+ grains) | Every 6 months | Sediment accumulates at double speed or worse |
| You hear popping/rumbling when it heats | Flush now | That sound is water boiling up through an established sediment layer |
| Tankless (on-demand) unit | Descale every 12 months | Scale in the heat exchanger cuts efficiency and trips error codes |
| Tank is 10+ years old and never flushed | Ask a plumber first | A heavy sediment bed can hide corrosion; a flush can reveal (not cause) leaks |
The cost of skipping it
What skipping it costs: sediment forces the burner or elements to run longer for the same hot water (roughly 10–25% more energy as the layer thickens), makes the tank rumble and pop, burns out lower heating elements on electric units ($150–300 repair), and shortens the tank's life by years. A replacement water heater installed runs $1,200–2,000+ — and they rarely fail at a convenient moment. An annual flush is free (DIY) or a modest add-on to a plumber visit.
How to do it (45–60 minutes · DIY with a garden hose)
- Turn the heater off: gas dial to "pilot" (or off), or flip the breaker for electric. Let it cool for a couple of hours if you can.
- Shut the cold-water inlet valve on top of the tank.
- Connect a garden hose to the drain valve at the bottom and run it to a floor drain or outside (downhill).
- Open a hot tap somewhere in the house to break the vacuum, then open the drain valve and let the tank empty.
- Briefly reopen the cold inlet in bursts to stir and rinse out remaining sediment until the water runs clear.
- Close the drain, refill the tank (hot tap still open until water flows steadily), then restore power/gas.
- While you’re there: check the anode rod every 2–3 years — a $30–60 rod is what stands between the tank steel and rust.
Knowing the interval is the easy half. OnOtto reminds you at the right interval — and won't let you snooze it into next year. Tasks persist until they're done, and completing the water heater flush schedules the next one automatically.
Put this on autopilot — free for 30 daysFrequently asked questions
Is it true you shouldn’t flush an old, never-flushed water heater?
Partly. Flushing doesn't damage a tank, but on a 10+-year-old tank a thick sediment bed can be plugging pinhole leaks or hiding corrosion — draining it can reveal problems that were already there. If the tank is old and has never been serviced, have a plumber assess it (and price replacement) rather than discovering a leak on a Friday night.
How do I know if my water is hard?
Telltales: white scale on faucets and shower glass, soap that won't lather, and that popping sound from the tank. For a number, a $10 test-strip kit or your water utility's annual quality report gives hardness in grains per gallon — above 7 gpg counts as hard, and above 10 a softener starts paying for itself in appliance life.
Do tankless water heaters really need annual descaling?
Yes — more than tanks need flushing, in hard water. Scale forms directly on the heat exchanger, cutting efficiency and eventually triggering error shutdowns; many manufacturers make annual descaling a warranty condition. It's a 60–90 minute job with a small pump, two hoses, and 2–3 gallons of food-grade white vinegar or descaler, or a $150–250 plumber visit.
What’s the anode rod and when does it need replacing?
A sacrificial magnesium or aluminum rod that corrodes so the tank steel doesn't. Check it every 2–3 years (yearly in softened water, which eats anodes faster) and replace when it's more than half consumed or coated in calcium. A $30–60 rod swap is the single best way to push a tank past its 8–12-year average life.