How to Flush a Water Heater: Step-by-Step for Tank and Tankless

Maintenance
By Emergency Water Heater SLC Team · · Updated March 7, 2026 · 6 min read

Flushing your water heater is one of the simplest maintenance tasks you can do yourself—and it’s one of the most important. Mineral sediment accumulates on the bottom of the tank, reducing efficiency and accelerating anode rod corrosion. In Utah’s hard water, sediment builds up 2-3 times faster than in soft water regions. This 30-minute DIY task can extend your water heater’s life by years.

Quick Answer

Flushing removes sediment buildup that reduces heating efficiency and damages the tank. The process: turn off power, open the cold water supply, attach a hose to the drain valve, and drain until water runs clear. Takes 20-30 minutes. In Utah, flush every 5-6 months (instead of annually) due to hard water. Cost: $0 if DIY, $150-$250 if professional. Safety note: water from the drain is hot—use a bucket or hose directed to a safe drain.

What You’ll Need

  • Garden hose (attach to drain valve)
  • Bucket (to catch initial water)
  • Flathead screwdriver (open drain valve)
  • Work gloves (hot water)
  • Access to a floor drain or outdoor location to discharge water
  • That’s it—no special tools required

Step-by-Step: Tank Water Heaters

Step 1: Turn off the power
Gas: Turn the control knob to “Pilot.” Electric: Flip the breaker to “Off.” Allow the tank to cool slightly (5-10 minutes). Hot water draining is safer if the tank has cooled a bit.

Step 2: Turn off the cold water supply
Locate the cold water inlet valve (top of the tank). Turn it clockwise until it stops. This prevents new water from entering while you drain.

Step 3: Relieve pressure
Turn on a hot water faucet somewhere in your home (bathroom sink is fine). Leave it on for 30 seconds. This releases air pressure in the tank and helps it drain completely.

Step 4: Attach the hose
Connect a garden hose to the drain valve (a small spigot at the bottom of the tank). Direct the hose to a floor drain, sump pump, or safely outside. Water will be hot—be careful.

Step 5: Open the drain valve
Use a flathead screwdriver to turn the drain valve counterclockwise. Start slowly; water pressure may push it open quickly. Let it run into a bucket first to gauge temperature, then guide the hose flow.

Step 6: Drain 5-10 gallons
Let water flow for a few minutes. You’ll notice sediment (cloudy water, rust color). Drain until the water running out appears clearer—usually 10-15 minutes.

Step 7: Flush with cold water
Turn on the cold water supply valve (which you shut off in Step 2) for 2-3 minutes while the drain valve is still open. This circulates fresh cold water through the tank, loosening additional sediment. You’ll see another burst of cloudy water.

Step 8: Close and refill
Close the drain valve by turning it clockwise. Turn the cold water supply valve back on fully. The tank will refill automatically.

Step 9: Restore power
Turn the gas valve back to “On” or flip the electric breaker back to “On.” The heater will resume normal operation.

Step 10: Check the faucet you opened
Turn off the hot water faucet you opened in Step 3. This re-pressurizes the system.

Step-by-Step: Tankless Water Heaters

Tankless units accumulate sediment in the heat exchanger. Flushing requires a descaling solution.

Step 1: Turn off gas/power
Turn gas control to “Off” or flip the electric breaker. Allow the unit to cool.

Step 2: Attach descaling kit
Tankless units have inlet and outlet ports on the side. Attach a descaling pump kit (available at hardware stores, ~$30-$50) to these ports following the kit instructions.

Step 3: Run descaling solution
Pour descaling solution (citric acid or vinegar-based) into the pump reservoir. Run the pump for 1-2 hours. This dissolves mineral deposits inside the heat exchanger.

Step 4: Flush with clean water
After descaling, run clean water through the unit for 10-15 minutes to rinse out remaining solution.

Step 5: Disconnect and refill
Remove the descaling kit. Turn on the gas/power. The unit is now flushed.

Tankless flushing is more complex. Many homeowners hire a pro for this ($150-$200).

Utah Hard Water Considerations

Utah’s water hardness (150-250 GPG) means:

  • Sediment accumulates 2-3x faster than national average
  • Flushing every 5-6 months is essential (not annually)
  • Neglecting flushes accelerates anode rod failure

If you’ve never flushed your water heater and you live in Utah, sediment has likely accumulated significantly. Your first flush may run cloudy for 20-30 minutes. That’s normal—keep going until it clears.

Safety Notes

  • Hot water: The water from the drain is hot. Wear gloves and direct hose carefully.
  • Never open the drain valve fully at once. Start slowly to avoid a burst of pressurized hot water.
  • Don’t skip relieve pressure. Failing to open a faucet can cause the drain valve to pop open unexpectedly.
  • Close the drain valve fully after flushing. A leaky valve wastes water and damages floors.

When to Call a Pro

Call a plumber if:

  • The drain valve is stuck and won’t open
  • Water doesn’t run clear after 30 minutes of flushing
  • You see large chunks of sediment or rust
  • The heater is 10+ years old and has never been flushed (professionals use vacuum extraction)
  • You’re uncomfortable with the process

A professional flushing costs $150-$250 and uses powerful equipment to remove deeply embedded sediment.

Pre-Flushing Checklist

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Flushing is straightforward, but if you’d rather have a professional handle it, a licensed plumber can flush and inspect your entire system in under an hour.

Frequently Asked Questions

How often should I flush in Utah?
Every 5-6 months. Utah’s hard water requires more frequent flushing than the national recommendation of annually.

What if the water won’t run clear?
Sediment may be heavily packed. Continue flushing for up to 30 minutes. If it still won’t clear, the tank may have extensive buildup—call a professional for vacuum extraction.

Can I flush while the heater is on?
No. Always turn off power and gas first. The heater must be off during flushing.

Is the water I drain safe to use in gardens?
The water is fine for outdoor use (plants, lawn irrigation), but don’t use it indoors—sediment could clog fixtures.

How do I know if my hose is connected properly?
The hose should screw onto the drain valve snugly. If water sprays out from the connection, tighten it more.

Sources and Update Policy

This article reflects step-by-step flushing methods for 2026, including Utah hard water adjustments.

We update this article annually with new flushing tools and descaling products available.

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