Draining Hot Water Heaters (Sediment)

The single thing that most water heater owners have in common is that they know they're supposed to "drain their tanks" to extend their lives. That's in the water heater instructions and it's because of sediment buildup. But that advice falls short, for reasons you'll understand as you read this page on what causes sediment, what it does to water heaters, and the possibilities for effectively getting rid of it.

"I had to replace my water heater last year. When I drained the old tank, a lot of sand came out."

Our friend had a close encounter with sediment. It wasn't sand in his water heater, although the two sometimes bear a close resemblance. It was calcium carbonate, a mineral present in water which the heat causes to precipitate out, and which settles into the tank bottom, where it does all kinds of bad things.

High on the list is forming a layer of insulation between the gas burner and the water. The sediment slows heat transfer and overheats the tank bottom. Overheating weakens the steel and damages the glass lining, hastening the day when the tank will fail altogether. In the case of electrics, it can bury the lower element, causing it to burn out. It also creates a playground for corrosive anaerobic bacteria. In addition, it lowers the energy efficiency of the tank.''

Sediment

Sediment can drift into recirculation lines, jam open check valves, and cause the recirculation pump to stick until it burns out. Finally, it causes noise, sometimes enough noise to annoy, or even frighten, people if the tank is inside a dwelling. The noise is caused by small amounts of water under the sediment layer turning to steam bubbles, which then collapse violently. Water heater makers have not done their customers many favors toward controlling sediment. The cold-water inlet, called a dip tube, is straight on many water heaters made today. That means the water strikes the bottom of the tank and causes the sediment to settle evenly on it instead of making it gravitate toward the drain.

Most manufacturers boast "self-flushing" dip tubes that supposedly keep the water so stirred up that sediment doesn't have a chance to settle. We have our doubts about these and prefer to actually eject sediment from a water heater. Also the flue that runs down the center of gas-fired tanks creates an additional obstacle to sediment removal. Most tanks, both gas and electric, have domed bottoms so that sediment falls out toward the edges and stays there. Standard drains are minuscule plastic affairs that can easily be clogged by one large flake of sediment. However, a brand new tank can easily be perforated before it's installed. That involves removing the drain valve and installing a brass 3/4-inch ball valve and hose adapter. The straight dip tube can be pulled out and a combination curved dip tube and nipple installed. The curve makes the water swirl the sediment around the flue and toward the drain. A tank so fitted can be flushed by simply hooking up a hose twice a year and letting the water run for 4-5 minutes. This is also a good time to install a second anode on the hot side (a combination anode/hot-water outlet rod). Tanks can also be retrofitted, but it's more complicated. A tank that's been in service six to seven years can present problems. If galvanized nipples were used, those can rust on the inside and break off. The plastic drain valve may have become brittle with heat and time and snap off. That doesn't have to be a catastrophe, but it can be quite disconcerting to find yourself staring at a broken valve while 40 gallons of hot water are pouring out. The mechanically inclined are welcome to attempt it, but another possibility is to print out the information and instructions from this site and hire a plumber to do it.

There are also chemical applications for removing sediment. Some are dangerous, all are time-consuming.