How to Flush Your Water Heater
Updated February 20, 2026
Flush sediment from your tank water heater to cut energy bills, eliminate rumbling noises, and add years to its life -- the most important maintenance task most homeowners skip.
Overview
Sediment is what kills water heaters. Minerals in the water settle to the bottom of the tank over time, forming a layer that insulates the water from the burner or heating elements. The heater works harder, your energy bills go up, recovery gets slower, the tank starts rumbling, and eventually the whole thing fails early. A tank that never gets flushed lasts 8-10 years. Flush it once a year and you are looking at 15-20. The whole process takes 30-60 minutes, costs nothing, and requires no special tools.
What You'll Need
Safety First
- The water in the tank is 120-140+ degrees. What comes out of the drain valve and hose will scald you on contact. Wear gloves, keep kids and pets away, and watch where you point the hose.
- Gas heater: turn the gas control to 'pilot' or 'vacation' before draining -- do not leave the burner firing on an empty or partially drained tank. That damages the tank lining.
- Electric heater: kill the breaker before draining. Heating elements exposed to air (not submerged) burn out within minutes. Do not flip the breaker back on until the tank is completely full and you have confirmed water at a hot tap.
- Never been flushed and the heater is 5+ years old? The drain valve may be partially clogged with sediment. Be ready for slow draining or a valve you need to work open gradually.
Step-by-Step Instructions
-
Turn Off the Heat Source
Gas heater: turn the gas control knob to 'pilot' (keeps the pilot lit but stops the burner). Electric heater: flip the breaker off at the panel. Critical step -- you cannot heat an empty tank. On gas models, keeping it on pilot means you do not have to relight afterward.
Tip: Not sure which breaker is the water heater? Look for a double-pole (240V) breaker labeled 'Water Heater' or 'WH' -- typically 30 amps. When in doubt, flip it off and confirm no hot water is being produced. -
Connect a Garden Hose to the Drain Valve
Find the drain valve near the bottom of the tank -- looks like an outdoor hose bib. Connect a garden hose and run the other end to a floor drain, driveway, or outside where scalding water can discharge safely. The hose needs to run downhill from the tank. No nearby drain? You may need to run the hose upstairs and outside, or use a utility pump. Do not drain onto grass or plants -- the temperature kills them.
Tip: Before you open the drain valve, open a hot water faucet somewhere in the house (a bathtub works well). This breaks the vacuum in the tank and lets water flow freely. Skip this step and the tank drains painfully slow or not at all. -
Drain the Tank
Open the drain valve counterclockwise. Water starts flowing through the hose -- it will probably be brown, rust-colored, or cloudy with visible sediment. That is exactly what you want to see. A 40-50 gallon tank takes 15-30 minutes to drain. While it is draining, turn the cold water supply on and off in short bursts (30 seconds on, 30 seconds off) to stir up sediment stuck to the bottom. Keep going until the water from the hose runs clear.
Warning: Drain valve clogged and barely trickling? Do not force it. Sediment is blocking the opening. Try opening and closing the valve a few times to knock the blockage loose. If it is a cheap plastic gate valve (common on budget water heaters), it may be permanently stuck -- a plumber can swap it for a brass ball valve on the next service call. -
Flush with Cold Water
With the drain valve still open, turn the cold water supply fully on. This sends a rush of cold water through the tank that stirs up and flushes out sediment stuck to the bottom. Let it flow through and out the hose for 5-10 minutes, or until the water runs completely clear. This is the real flushing -- draining alone removes water but does not dislodge the sediment that is baked onto the bottom. The cold water agitation is what actually cleans the tank.
Tip: Seeing large chunks or heavy sediment even after several minutes? The tank has serious buildup. Keep flushing. Tanks that have never been flushed can take 15-20 minutes of cold water flow before the water runs clean. -
Refill the Tank
Close the drain valve (clockwise until snug, do not crank). Disconnect the hose. Make sure the cold water supply is fully open -- the tank starts refilling. Go to the hot faucet you opened earlier and let it run. It will sputter and spit air at first -- that is normal, just air purging from the tank and pipes. Once you get a solid, steady stream with no air bursts, the tank is full. Close the faucet. Check the drain valve for drips -- if it weeps, tighten slightly or thread a brass hose cap onto it as a backup seal.
Warning: Do not turn the heat back on until the tank is completely full and you have confirmed a steady stream at a hot faucet. Firing the burner or energizing elements in a partially empty tank can crack the lining, burn out elements, or cause a dangerous steam pressure event. -
Restore the Heat Source and Verify
Gas heater: turn the gas control from 'pilot' back to your normal temperature setting (120 degrees is recommended). You should hear the burner fire. Electric: flip the breaker back on. Wait 30-60 minutes for the water to heat up, then test a hot faucet. Check the drain valve one last time. Done.
Tip: First heat cycle after the flush will take longer than usual because the entire tank is starting from cold. That is normal. If you notice the water heats faster and the tank is quieter than before -- that is the sediment removal doing its job.
Pro Tips
- Once a year minimum. Every 6 months if you have hard water. Annual flushing is the single biggest factor in whether your tank lasts 8 years or 20.
- While the tank is drained, test the T&P (temperature and pressure) relief valve. Lift the lever, let it snap back. You should hear water flow briefly into the discharge pipe. If nothing happens or it does not reseat, replace it -- $15-25 part and an important safety device.
- Got a cheap plastic gate valve for the drain? Have a plumber swap it for a brass ball valve on the next service call. Ball valves are more reliable, less likely to clog, and make every future flush easier.
- A sediment trap (flush kit) on the cold water inlet catches minerals before they enter the tank. Reduces buildup between flushes and extends the time between necessary drain-downs.
- Rumbling, popping, or cracking noises from the tank? That is sediment on the bottom being heated until it pops. Flushing eliminates it. If the noise continues after a thorough flush, the sediment has hardened and the tank is nearing end of life.
When to Call a Pro
This is straightforward DIY. But call a plumber if the drain valve is stuck or broken, if the tank has never been flushed and is over 10 years old (heavy sediment can clog the valve mid-flush), if you smell gas at any point, if the T&P valve is leaking or will not reseat, or if you are not comfortable relighting a gas pilot.