Why bother
Draining a water heater isn't glamorous and nobody asks you about it. But in a place with moderately hard water, which is what the North Texas Municipal Water District describes for Rowlett, it's the one job that most affects how long a tank runs and how much it costs to run. It takes half an hour, a hose and a bucket, and it's the sort of thing that's easier to do every year than once, late, in a panic.
What you're removing is sediment. Hard water carries dissolved minerals, mostly calcium and magnesium. When the water is heated, some of those minerals come out of solution and fall to the bottom of the tank, where they build up as a gritty layer. Left alone, that layer insulates the water from the burner or element, makes the heater run longer, and causes the popping and rumbling that people notice.
Before you start
Check you have the right tank for this. A standard gas or electric tank with a drain valve near the bottom is a good candidate. If the heater is older than about eight years and has never been flushed, be careful: the valve can be clogged or stuck, and some tanks, once disturbed, start to leak at the drain. If you're not sure, call someone.
You'll need a garden hose long enough to reach a floor drain or the outside, a bucket for testing, and gloves. Water from the tank can be hot enough to scald, so let it cool first, or at least don't stand beside the hose end. Pick a time when no one needs hot water for an hour or two.
A gentler start: the quarter flush
If the tank has never been flushed and it's a few years old, don't begin with a full drain. Start small. With the power off and the cold-water valve open, attach the hose and run a couple of gallons into a bucket. Look at it. Run another couple of gallons. If the water is clear after a few buckets, the tank is clean and a full flush isn't urgent. If it's cloudy or gritty, keep going.
This lets you see what you're dealing with before you commit to emptying the tank. It's also kinder to an old drain valve, which gets used less. If you do this once a year, you won't need to do more.
The steps
- Turn off the power. For an electric heater, switch off its breaker. For a gas heater, turn the gas control to pilot or off.
- Close the cold-water valve on the pipe above the heater.
- Connect the hose to the drain valve near the bottom of the tank and run the other end to a drain or outdoors, downhill from the tank.
- Open a hot tap somewhere in the house, ideally upstairs. This lets air in so the tank can drain.
- Open the drain valve and let the tank empty. It can take 20 minutes or more.
- With the tank empty, open the cold-water valve for a few seconds at a time and let it flush through, then close it. Repeat until the water coming out is clear.
- Close the drain valve and disconnect the hose. Close the hot tap, open the cold-water valve and let the tank fill. Leave a hot tap open until water runs steadily, to push the air out of the system.
- Only when the tank is full, turn the power or gas back on.
Do not turn an electric heater on while the tank is empty. The elements burn out within seconds when there's no water around them. It's the most common mistake in this job.
What you'll see
The first water is often cloudy, gritty or tinted. It may carry small flakes of scale or sand. That's the sediment you're after. Keep flushing until the water runs clear. If it runs clear in a minute, the tank is in good shape. If it takes ten minutes and keeps coming out brown, the layer is thick.
A few other things to note. If the flow slows to a trickle, the valve is clogged with sediment. Opening and closing it can sometimes clear it, but don't force a stuck handle. A plastic drain valve can crack, and an old brass one can seize. If the water that comes out is rust-red and doesn't clear, the tank may be corroding inside and replacement is on the cards.
While you're there
Look at the relief valve and its discharge pipe on the side or top. Lift the lever briefly with a bucket under the pipe, and let it snap back. Water should come out and then stop. A valve that doesn't open or doesn't reseat needs replacing. Check the pipe for stains or corrosion at the connections.
Look at the floor around the base of the tank for rust rings or damp. Check the gas connection for soot or scorch marks, and the vent for any staining. If there's a cap on top over the anode rod, note how it looks, because a rod used up in three to five years is common in hard water and swapping one is a job worth doing.
The anode rod: checking it and swapping it
The anode rod is the part that most tanks never get looked at. It screws into the top of the tank, usually under a hex head or a plastic cap, and it takes most of the corrosion so the steel doesn't. In hard water it can be eaten away to a thin wire in three to five years.
To check it, turn off the power or gas, close the cold supply, drain a few gallons so the water level drops below the rod, and unscrew it with a long socket and a breaker bar. They're often tight. You need clear space above the tank, about a foot, though a flexible rod can be bent in where there's less room. A good rod is thick and still covered with metal. One that's pitted, thin or bare steel along its length is done.
A new rod costs little next to a tank. Fitting one is a plumber's job if you aren't comfortable with it, and in an attic or a closet with a low ceiling it's a good reason to ask for help. It's the single most effective thing you can do to push a tank towards the top of its 8 to 12 year range.
How often
Once a year is a good habit in Rowlett. In a house with softened water, less often can be fine. If the heater has never been flushed and is under eight years old, start with a partial flush, running only a few gallons off the bottom, and see what comes out. If the tank has run for ten years with no flush at all, think of it as a tank near the end, and the money may be better spent planning a replacement.
The post on how long a water heater lasts in North Texas explains the anode rod and what else wears a tank out.
Keeping a simple record
Write the date of each flush on a piece of tape on the tank, or in your phone. Note what the water looked like. Next year you'll know whether the sediment is getting worse or staying put, which tells you more about the tank than any single look. If the notes show the water getting dirtier every year, the tank is on its way out, and you'll know in time to choose your day.
The post on how long a water heater lasts in North Texas has a rough timeline that fits those notes.
Tankless units need it too
A tankless heater has no tank to drain, but the same minerals coat the inside of the heat exchanger as scale. Over time that reduces flow and efficiency. The fix is a periodic flush with a pump and a mild descaling solution through the service valves, typically once a year in hard water. A tankless unit installed without those valves is hard to flush later, which is one reason we fit them on every tankless job.
When to hand it to a plumber
If the drain valve is stuck, leaks when you touch it, or the tank has never been flushed and is over eight years old, it's worth getting someone to do it, or to decide whether the tank is worth saving. A stuck valve is a small job for a plumber and a big problem for a tank that starts leaking from a forced one.
And if you flush it and the answer from the tank is rust, sludge and a rumble, you've learned something useful. Our replacement page shows what a swap involves, and the signs of a failing heater will help you decide whether it's time.