How often should I flush my water heater?

Once a year is the standard recommendation. If you have hard water (common across the Midwest, Southwest, and much of Florida and Texas), every six months. If it has never been flushed and is more than 5–7 years old, see the caution in this guide before draining it.

Can flushing an old water heater cause it to leak?

It can. On a tank that has never been flushed, sediment can be plugging small corrosion spots. Draining removes the sediment and the leak appears. The leak was coming anyway; flushing just revealed it. If your tank is over 10 years old and has never been flushed, be prepared to replace it soon regardless.

Does this apply to tankless water heaters?

Tankless units need a different procedure: a descaling flush with white vinegar circulated by a small pump through the isolation valves. It takes about an hour and a $25 pump kit, and most manufacturers require it annually to keep the warranty.

Should I replace the anode rod at the same time?

Check it every 2–3 years. The anode rod is a sacrificial metal rod that corrodes so the tank does not. When it is down to the bare wire, a $20–$40 replacement can double the remaining life of the tank. It usually takes a 1-1/16 inch socket and a breaker bar.

How to Flush Your Water Heater (and Why It Saves You Money)

Every gallon of water that enters your water heater carries dissolved minerals. When the water is heated, some of those minerals drop out and settle at the bottom of the tank. After a year that is a layer of sand-like sediment; after five years in a hard-water area it can be several inches of rock-hard scale.

That layer sits between the burner (or lower heating element) and the water. The heater has to burn longer to push heat through it, the tank bottom overheats and weakens, and on gas units you may hear a popping or rumbling sound as water trapped under the sediment flashes to steam.

Flushing removes it. The whole job is 30–45 minutes, and you need a garden hose.

Before you start

Check the age. The serial number sticker has a manufacture date, sometimes coded (the manufacturer’s website decodes it). Most tanks last 8–12 years.

If the tank is over 10 years old and has never been flushed, understand that draining it may reveal a leak the sediment was hiding. It is still worth knowing — better a controlled discovery on a Saturday than a flooded basement in February. Just have a plan.

You will need:

A garden hose long enough to reach a floor drain, utility sink, or outside
A flathead screwdriver (many drain valves have a slot instead of a handle)
A bucket
30–45 minutes, mostly waiting

Step-by-step

Step 1: Turn off the heat source

Gas: turn the control knob to Pilot (or Vacation) so the burner won't fire while the tank is empty. Electric: turn off the breaker. Running an electric element with no water around it destroys it in seconds.
Step 2: Turn off the cold water supply

The valve is on the cold inlet pipe at the top of the tank. Turn it clockwise until it stops.
Step 3: Open a hot water faucet upstairs

This lets air into the system so the tank drains instead of holding a vacuum. A bathtub faucet works well.
Step 4: Connect the hose to the drain valve

The drain valve is near the bottom of the tank. Run the hose to a floor drain, a utility sink, or outdoors. Keep the hose end lower than the valve. The water will be hot — keep kids and pets away from the outlet.
Step 5: Open the drain valve and let it run

Open the valve fully. Expect discolored water at first, then a stream of sediment. Let it run until the tank is empty (10–20 minutes for a 40–50 gallon tank). If flow stops early, sediment is blocking the valve — briefly open the cold supply to stir it up, then close and continue.
Step 6: Flush with cold water

With the drain valve still open, turn the cold supply on for 1–2 minutes to stir and flush remaining sediment. Repeat until the water runs clear into the bucket. This is the step most people skip, and it's where most of the sediment actually leaves.
Step 7: Close the drain, refill, then restore heat

Close the drain valve, remove the hose, and open the cold supply. Leave the upstairs faucet open until water flows steadily with no sputtering — that means the tank is full. Only then turn the gas back to On (relight the pilot if needed) or flip the electric breaker back on.

Troubleshooting

The drain valve won’t close or drips afterward. Cheap plastic drain valves are notorious for this. A brass hose cap ($3) screwed onto the valve stops the drip until you replace the valve with a brass ball valve ($15, a 20-minute job when the tank is next drained).

Only a trickle comes out. The sediment layer is above the valve. Close the drain, open the cold supply for 30 seconds to stir the tank, then try again. If still blocked, a wet/dry vacuum on the open drain valve can pull the plug loose.

Popping or rumbling continues after flushing. The scale is hardened onto the tank bottom. Some plumbers use a de-liming solution; often this is a sign the tank is near end of life.

While you’re there: the two-minute upgrades

Set the temperature to 120°F. Most tanks ship at 140°F. Lower is safer and saves $35–$60 a year.
Check the anode rod if the tank is 3+ years old. See the FAQ below.
Add a $25 insulation blanket if the tank is warm to the touch — that’s heat you’re paying for and losing.
Insulate the first 6 feet of hot and cold pipes with foam sleeves ($1 per 6-foot length).

Put a reminder on next year’s calendar. The second flush is faster than the first, and the tank will thank you with a few extra years.