Short answer: To flush a water heater, turn off the power or gas, shut the cold water supply, attach a hose to the drain valve, open a hot tap and drain the tank. Then briefly turn the cold water back on to stir and rinse out sediment until the water runs clear. Refill completely before restoring power. Most tanks need it yearly.
Flushing a water heater is one of the easiest ways to help it last longer. It clears out the sediment that settles at the bottom of every tank. This guide walks you through each step for gas and electric heaters. If you'd rather not do it yourself, our water heater maintenance service in Newark covers flushing and more.
Why flush a water heater?
Every gallon of water that enters your tank carries a little bit of dissolved minerals. When water is heated, some of those minerals settle to the bottom as sediment. Over time that layer:
- Makes popping and rumbling sounds on gas heaters
- Wastes energy by insulating the water from the burner
- Takes up space, so hot water runs out sooner
- Can burn out the lower element on electric heaters
- Speeds up corrosion of the tank bottom
Newark's city water is only slightly hard (around 80 ppm), so sediment builds slowly. Homes on harder groundwater, like many around Middletown, build sediment faster.
When you should not flush it yourself
Skip DIY flushing and call a pro if:
- The tank is over 10 years old and has never been flushed
- The drain valve is plastic and brittle, or already leaking
- The tank is already leaking
- You are not comfortable working with gas or 240-volt power
What you need
- A garden hose long enough to reach a floor drain, sump or the outdoors
- A flat screwdriver or adjustable wrench
- A bucket and towels
- Work gloves and eye protection
- About 1 to 2 hours
How to flush a water heater, step by step
Step 1: Turn off the energy
- Electric: Switch off the water heater breaker. This is critical. Running an empty tank will burn out the elements in seconds.
- Gas: Turn the gas control knob to "Pilot" (or "Off").
Step 2: Let the water cool (recommended)
Tank water can be 120°F to 140°F or hotter. Waiting a few hours, or using hot water for a while first, lowers the burn risk.
Step 3: Shut off the cold water supply
Turn off the valve on the cold pipe at the top of the heater.
Step 4: Connect a hose to the drain valve
Screw the hose onto the drain valve at the bottom of the tank. Run the other end to a floor drain, sump or outside, below the level of the valve.
Step 5: Open a hot water tap
Open a hot faucet in a nearby sink or tub. This lets air in so the tank drains smoothly.
Step 6: Open the drain valve
Open the drain valve slowly. The water may come out cloudy or with bits of sediment. Let the tank drain.
Drain valve stuck or leaking?
Stop and call us. A stuck valve is easy to break, and that turns a flush into a repair.
Step 7: Stir and rinse the sediment
Once the tank is mostly empty, briefly turn the cold water supply back on for a few seconds, then off again. This stirs up sediment so it flows out. Repeat until the water from the hose runs clear.
Step 8: Close the drain and refill
Close the drain valve and remove the hose. Turn the cold water supply fully back on. Leave the hot tap open until water flows out steadily with no sputtering air. That means the tank is full.
Step 9: Restore power or gas
- Electric: Only after the tank is completely full, turn the breaker back on.
- Gas: Turn the knob back to "On" and set the temperature. Relight the pilot if needed, following the label.
Step 10: Check for leaks
Look at the drain valve for drips over the next few hours. A small drip may stop with gentle tightening. If it doesn't, the valve may need to be replaced.
How to flush a tankless water heater (descaling)
Tankless units don't collect sediment the same way. They build up scale in the heat exchanger. Descaling is a different process:
- Turn off power and gas to the unit.
- Close the hot, cold and gas service valves.
- Connect a small pump and hoses to the service ports.
- Circulate a descaling solution or white vinegar through the unit, often for 45 minutes to an hour.
- Rinse with fresh water, clean the inlet filter and restore service.
Your unit needs service valves for this. If it doesn't have them, a pro can add them.
Bonus: check these while you're there
- Anode rod: If you can, check it every few years. Replace it if it's worn to the core wire.
- Relief valve: Lift the lever briefly to make sure water flows, then let it snap shut. If it drips afterward, it needs replacing.
- Temperature: About 120°F is safe and efficient for most homes.
How often should you flush?
| Home situation | Suggested schedule |
|---|---|
| City water in Newark (slightly hard) | About once a year |
| Hard well water or Middletown groundwater | Every 6 to 12 months |
| Tankless heater | Descale about once a year |
| Water softener installed | About once a year, check the anode more often |
Regular flushing is one of the best ways to help a heater reach the upper end of its life. See how long do water heaters last?
Local note: Harder municipal water in Middletown and private wells near Hockessin fill tanks with sediment faster than Newark's city water. In Pike Creek condos, closet tanks often lack a nearby drain, so plan your hose route first.
Related reading: Check the water heater anode rod while the tank is partly drained, learn how long water heaters last, and use our no hot water troubleshooting guide if the heater acts up after a flush.
When should you call a water heater professional?
Call a pro if:
- The drain valve is stuck, cracked or leaking
- The tank is old and has never been flushed
- You have no hot water after flushing
- You want the anode rod and relief valve checked too
- Your tankless unit shows a scale or flow error code
Need a water heater flushed in Newark? Call (302) 732-0874 to book water heater maintenance with Newark Heater Pros.
Frequently asked questions
How often should I flush my water heater?
Most manufacturers recommend about once a year. Homes on hard well water may benefit from flushing every six months.
What happens if I never flush my water heater?
Sediment builds up at the bottom of the tank. That can cause popping noises, lower efficiency, less hot water and a shorter tank life. On electric heaters, it can burn out the lower element.
Can flushing an old water heater cause a leak?
Sometimes. On a tank that has never been flushed, opening the drain valve can stir up sediment and keep the valve from sealing again. On very old tanks, it's best to have a pro check the condition first.
Can flushing a water heater cause a leak?
It can reveal one. On old tanks, moving sediment or opening a brittle plastic drain valve may lead to a drip that was waiting to happen. If the tank is over 10 years old and never flushed, have a pro look first.
How long does it take to flush a water heater?
Plan on about an hour for a tank, including cooling time. A tankless descaling usually takes about 45 minutes to an hour with a pump and solution.
Sources
- U.S. Department of Energy: Energy Saver Guide (PDF)
- U.S. DOE Building America: Transitioning to a Tankless Water Heater (PDF)
- ENERGY STAR: Heat Pump Water Heater Installation Best Practices
- U.S. Consumer Product Safety Commission: Avoiding Tap Water Scalds (PDF)
- WaterHardness.org: Newark, DE water hardness by utility
