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Know the flow: a guide to water heater preventive maintenance: typically, property managers have little reason to be concerned with water heaters unless they rust, leak or explode. With regular preventive maintenance, such costly and catastrophic events can be avoided.

It was an almost perfect launch. It soared straight upward, curved gracefully out over the freeway and touched down about 500 feet away. The only problem was, it wasn't a rocket. It was a water heater. It also left a big hole in the roof, a half-million dollars in damages and four injured people in its wake.

Happily, water heaters do not explode every day. That's a good thing because when one does, it's usually catastrophic. Sometimes even fatal.

In houses, apartments and business across America, the lowly water heater serves its masters--usually in the dark--ignored, misunderstood, unloved.

No one is expected to shed tears or start writing sonnets to their water heaters, and they will never occupy the same warm spot in their hearts as Fido, but water heaters at least should be understood, because understanding brings big benefits. Part of understanding water heaters is not ignoring them.

Major safety, liability and cost issues are involved. Some of these issues exist from the start, while others develop over time. And for property owners with big, expensive tanks or numerous small ones, the stakes are commensurately higher.

The Temperature/Pressure Relief Valve

Let's start with our exploding water heater. How did it happen? This case, written up in the April 2002 edition of the Journal of Light Construction, occurred because someone installed a big electric water heater without a temperature/pressure relief valve--known as a "T&P" in the plumbing trade. That valve is there to open and vent excess pressure--or even steam--if the burner on gas heaters or elements on electric tanks fail to shut off.

If it is not there, or does not function, then the water temperature and pressure will rise until they crack the tank. At that moment, all the water inside will flash instantaneously into steam and expand to about 1,700 times its original volume, putting an observer at ground zero for a moon launch. Is this scary? Good!

T&Ps should be tested yearly by pulling up on the handle to see if water will flow when the valve is opened and stop running when it is shut, by letting go of the handle. If it does nothing, runs or drips, the valve should be replaced.

Hardly anybody tests T&Ps. Why? Because about 25 percent of them fail the test and must be replaced. This is a bother, of course, but then, so is that hole in the roof.

There are several other important issues relating to T&Ps. The first is that there should always be a pipeline running from the valve, at a minimum, down toward the floor. The purpose is to prevent your face from landing in the bum ward if the valve opens while standing next to it.

The second is that the line should generally go down and out, without obstruction. We have lost track of the times we have found them plumbed uphill. That's usually because a shorter tank replaced a taller one, or a water heater with the T&P on the side replaced one with the valve on the top and because the drain line went to the outside through a wall, it was easier to connect to the old line than cut a new hole lower in the wall and do it right.

The third issue is that a probe that extends from the bottom of the T&P must actually go inside the tank. In some cases, they are mounted in piping a couple of feet out of the tank. For those, the heater would be on its way to the moon before the valve realized it was supposed to open.


However, if the water heater has not launched through the roof lately and it is gas-fired, it probably still has a vent pipe running from the tank to the outside; but, maybe not. We have found a good dozen cases where the vents had fallen off the water heaters and toxic exhaust gases, including carbon monoxide, were venting underneath, adjacent or even in someone's apartment.

Carbon monoxide cannot only kill, but sicken and cause brain damage.

There are two issues here. One is that nobody had looked in on these water heaters for a long time. And the other is that the vent segments had either merely been crimped and shoved together or taped. Sadly, duct tape isn't really that great for ducts. It occasionally comes loose. Screws should be used.

There are other issues related to vents. One is proper sizing. That could be the subject of a whole additional article--although perhaps not the most exciting one. Suffice it to say that not just any old thing will do. Vent diameters must match and if smaller ones merge in a larger one, there are rules for that, too.

If those rules are violated, exhaust gases might come back into the water heater space. That's called backdrafting. It can even eat up vent pipes with an acidic condensation.

Soot, Water and Rust

Another potential cause of flue gases spilling out of the heater is soot in the combustion chamber of gas heaters and their flues. How did it get there? Well, gas water heaters breathe. They draw air from underneath to combust the gas. If the floor isn't clean, lint or dust can be sucked in, foul the burner, cause the gas to burn incompletely, and voila, soot is formed.

The biggest cause of soot is laundry room lint. But plain old dirt or diatomaceous earth in pool rooms will do it, too. Floors should be vacuumed on a regular basis because de-sooting a commercial water heater is not easy nor cheap--costing several hundred dollars.

But why bother? If the soot gets bad enough, it turns into a fire hazard. The flues will not draw properly and before long, fire starts billowing out the bottom, igniting anything nearby.

Without question, water heaters are primal: earth, air, fire, water.

Speaking of which, water can be an issue no matter which type of tank it is. The kind of water of concern here is leaking water.

Water heaters are connected to plumbing with dielectric copper flex lines or unions. Both have rubber gaskets that will shrink with heat. The fittings should be tightened a bit after six months, or they can leak, allowing water to run down onto the tank.

A water heater has considerable protection against rust inside, but there is nothing to prevent rust from forming outside. It can be damaged very quickly by water dripping onto it. Badly soldered plumbing will do the same. And it does not even have to be a leak. In one example, the flue gases backdrafted against a coldwater line, causing enough condensation to drip down and rust trough the cover. The tank has survived for now, but only time will tell. Insulation and better venting could have prevented it.

Then there is the water temperature. A temperature of 110 degrees is low enough to let legionella bacteria grow in a tank, and a temperature of 190 degrees is hot enough to instantly scald a hand off.

Legionella bacteria cause Legionnaire's disease and can be inhaled as mist by people who are taking showers. It is serious business, even if people do not die from it. A recent study found that people suffered lingering aftereffects a year and a half after recovery.

The preferred temperature setting is 130 degrees. That is hot enough to banish the bacteria, but low enough to avoid scalding.

Actually, scalding can happen at 130 degrees, but it allows time to draw back. (Note: If the water heater serves people with immune system problems, the temperature may need to be 5 degrees to 10 degrees above the 130 mark.) Check the water temperature at the tap with a meat or candy thermometer. Higher temperatures also use more energy and nearly double the amount of sediment buildup with each 20-degree rise.

And, statistics show that scalding injuries are primarily falls, not burns, as people draw back from the hot water.

Recirculation Pumps

One final safety issue is residents' access to water heater spaces. Generally, tanks and people do not mix especially well. Water heater closets should be in closed confines and locked.

There are other issues besides safety that affect the pocketbook. One is whether recirculation pumps are working. Recirculation pumps are installed to ensure that those farthest from a water heater have prompt hot water, since water sitting in the plumbing between the tank and the tap is constantly cooling off. They also cut water usage, since people do not have to run the tap to draw hot water through the lines from the tank.

Some pumps also have thermostats designed to shut them off during slack periods and cut energy loss from the pipes. Those should be set 20 degrees below the tank thermostat setting or they'll never work.

One would think that residents would complain when a pump bums out, but that is not always the case. Recirculation pumps run whisper-quiet. Dead pumps share that characteristic.

To check the operation, put one end of a long screwdriver on the pump and the handle up to your ear and listen; by checking the piping upstream and below the pump to see if it is warm (piping higher than the pump can be heated by convection from the tank); and finally, the acid test, by going to the farthest unit in the recirculation loop and seeing how long it takes to get hot water.


A broken recirculation pump is bad, but a broken water heater can be a disaster if it is installed inside an apartment home or where it will flood the home if it breaks. In that case, at minimum it should be installed on a drain pan that has a drain line leading out to a sidewalk or some other place where water running from it can be spotted. That way, the tank can be replaced before the leak becomes huge.

Another way to prevent flooding is to simply make sure the tank never breaks. How? By dealing with the two issues that control longevity.

Lots of people know about one: calcium carbonate sediment buildup and the need to eliminate it. Few know about the other--sacrificial anodes--although they have been an integral part of water heater construction for more than 50 years.

A water heater is simply a steel tank with vitreous glass bonded to the interior to prevent rust. The glass lining protects most of the tank, but due to limitations in the manufacturing process, there is still a little bit of steel that is exposed. For prevention's sake, one or more sacrificial anodes are installed to protect that steel by slowly corroding. When there is little left of them, the tank starts to rust and ultimately fails.

Residential tanks typically have one anode in a six-year-warranty tank, or two in a 12-year-warranty heater. One way to cut flooding risk is to buy a 12-year-warranty water heater. Another is to buy a 6-year-warranted one and add a second anode. These cost much less than the price premium on the 12-year tank.

Typically, anodes cannot be added to a commercial water heater, but they can be checked and replaced. Cleaning out sediment also is recommended. Tanks that receive the prescribed service can last the life of the building. This service also provides an opportunity to make sure no hazards have developed and that recirculation pumps and T&Ps are functioning properly.

Then lowly water heaters will continue to serve in an unsung fashion--instead of making the 6 p.m. news headlining fire, flood and disaster.

Randy Schuyler is a water heater consultant and journalist. He is based in Marina, Calif., and can be reached at 831/917-0850 or via e-mail at
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Author:Schuyler, Randy
Date:Jun 1, 2003
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