Is It Better to Flush or Drain Your Water Heater? The Right Way to Maintain It

Every year, thousands of water heaters fail prematurely-not because they’re broken, but because no one ever cleaned them. If your water heater is more than five years old and you’ve never flushed or drained it, you’re probably sitting on a tank full of rust, sand, and mineral buildup. The question isn’t whether you should do it-it’s whether you should flush or drain it. And the answer isn’t as simple as it sounds.

What’s the difference between flushing and draining?

People use the words "flush" and "drain" like they mean the same thing. They don’t. Draining is just letting the water out. Flushing is actively moving water through the tank to push out sediment. You can drain without flushing. But you can’t flush without draining first.

Think of it like washing a coffee mug. Draining is pouring out the leftover coffee. Flushing is running water through it while scrubbing the inside to get the gunk off the bottom. Your water heater needs the scrubbing part.

Why sediment is killing your water heater

Hard water is common in New Zealand-especially in places like Wellington, Christchurch, and Hamilton. That means your tap water carries calcium, magnesium, and iron. When you heat that water, those minerals drop out and settle at the bottom of the tank. Over time, they build up into a thick, cement-like sludge.

This sludge does three things:

• It traps heat, forcing your heating element or burner to work harder. That raises your electricity or gas bill.
• It creates hot spots that burn out the tank lining. That leads to leaks.
• It clogs the drain valve. When you finally need to drain it, the valve won’t open-or it breaks off.

A 2023 study by the New Zealand Plumbing Institute found that water heaters with heavy sediment buildup failed 40% faster than those maintained yearly. That’s not a myth. That’s science.

When to drain your water heater

You should drain your water heater at least once a year. If you live in a hard water area, do it twice-once in spring, once in autumn. Signs you’re overdue:

• Your water smells like rotten eggs (that’s sulfur reacting with bacteria in the sludge)
• Your shower water is cloudy or discolored
• You hear popping or rumbling noises when the heater turns on
• It takes longer than usual to heat up

Don’t wait until you’re out of hot water in the middle of winter. By then, it’s too late.

How to drain your water heater (step-by-step)

Draining is easy. You just need a garden hose and a bucket. Here’s how:

1. Turn off the power. For electric heaters, flip the breaker. For gas, turn the dial to "Pilot".
2. Shut off the cold water supply. Look for the valve on top of the tank-it’s usually labeled.
3. Attach a garden hose to the drain valve at the bottom. Run the other end to a floor drain, outside, or into a large bucket.
4. Open the drain valve. Let the water flow out. It’ll come out dirty at first-brown, orange, or gray. Keep going until it runs clear.
5. While draining, open a hot water tap somewhere in the house. This lets air in and helps the tank empty faster.
6. Once the water runs clear, close the drain valve, remove the hose, turn the cold water back on, and refill the tank.
7. Once full, turn the power or gas back on.

It takes about 20 to 40 minutes. You don’t need special tools. Just patience.

How to flush your water heater (the real clean)

Draining removes most of the sludge-but not all of it. To truly flush the tank, you need to stir up the sediment while water flows through.

Here’s how to do it right:

1. Follow steps 1-3 from the draining process above.
2. Open the drain valve and let water flow for 30 seconds.
3. Turn the cold water supply back on for 10 seconds. This creates a rush that stirs up the sediment at the bottom.
4. Turn the cold water off again. Let the tank drain for another 30 seconds.
5. Repeat steps 3 and 4 three to five times.
6. Keep going until the water runs completely clear-no cloudiness, no grit.
7. Close the valve, remove the hose, refill, and restore power.

This method is more effective because you’re not just letting gravity do the work-you’re using water pressure to shake loose the stuck-on crud. It’s the difference between rinsing a bowl and scrubbing it.

What not to do

Many people make these mistakes:

• Trying to drain without turning off the power-this can damage the heating element.
• Using a bucket that’s too small-the water comes out fast and hot. A 10-liter bucket will overflow in seconds.
• Forgetting to open a hot water tap upstairs-this traps air and slows drainage.
• Trying to force a stuck drain valve with pliers. That’s how valves break. If it won’t budge, call a plumber. Don’t risk flooding your garage.

And never, ever skip the refill step. If you turn the power back on while the tank is still empty, you’ll burn out the element or warp the tank. That’s a $1,200 mistake.

Flushing vs. draining: which is better?

Draining is better than nothing. But flushing is what keeps your heater alive for 15+ years.

Here’s the reality:

Comparison: Draining vs. Flushing Your Water Heater

Feature	Draining Only	Flushing (With Stirring)
Removes loose sediment	Yes	Yes
Removes stuck-on sludge	Partially	Yes
Improves efficiency	10-15%	20-30%
Extends tank life	2-4 years	5-8 years
Prevents valve clogs	Low chance	High chance
Time required	20-30 min	40-60 min

If you want your water heater to last past its warranty, flush it. Not just drain it.

What if your drain valve is stuck?

It happens. Especially in older tanks. If the valve won’t turn:

• Don’t use pliers. Use a wrench with a longer handle for more leverage.
• Try tapping the valve lightly with a rubber mallet. Sometimes that breaks the corrosion seal.
• If it still won’t move, turn off the water and power, then call a plumber. They can replace the valve without draining the whole tank.

Some plumbers offer a "sediment flush service" for $80-$120. That’s cheaper than replacing a broken heater. And they’ll do it right.

What about tankless water heaters?

Tankless units don’t store water, so they don’t collect sediment the same way. But they still need cleaning. Mineral buildup can clog the heat exchanger. Most manufacturers recommend flushing them with vinegar or a descaling solution every 6-12 months. Check your manual. The process is different-it’s a closed-loop system with a pump. Don’t try to drain it like a tank heater.

How often should you really do it?

It depends on your water quality.

• Soft water (low minerals): Once a year
• Hard water (high minerals): Twice a year
• Well water (often iron-rich): Every 4-6 months

If you’re not sure, test your water. You can buy a simple hardness test strip from a hardware store for under $5. If the color reads above 7 grains per gallon, you’re in hard water territory.

Final tip: Write it on your calendar

Most people forget. Set a recurring reminder on your phone. Pick a date-say, the first Saturday of April and October. When that day comes, spend an hour doing this. You’ll save money, energy, and stress.

A water heater that’s flushed regularly can last 15 to 20 years. One that’s ignored? Maybe 8. That’s not a guess. That’s what repair technicians see every week.

Flush your water heater like you brush your teeth-regularly, without drama. It’s not glamorous. But it’s the reason your shower still works in January.