Bad things happen in water heater closets and boiler rooms when nobody is looking. Unions and piping can leak, temperature/pressure relief valves fail, recirculation pumps die, vent pipes fall, soot hazards develop. These are things that can harm your water heaters, damage your buildings, even kill your tenants! Everything should be checked at least every two years. For a look at some of the worst cases that we've found during our inspections, visit the Closet of Horrors.

Residential water heater closets should be checked at least once, especially if handymen* have done installations, tenants have access to the closets or there is a flood risk if a tank breaks. But absent these things, changes tend to occur more slowly with residential-type tanks than with commercial ones.

*This is not meant to be a dig against all handymen. We've known incompetent plumbers and super-competent handymen, but the latter are, by nature, jacks of all trades. We've known lots of such folks who replaced a tank and violated code because they didn't understand the "why" behind the "what."

We've developed a checklist of things to look for. Here is the what and the why.

What: Date of manufacture/installation, model number and who made the heater
Why: So you can keep track of how long a tank lasts and have warranty information if it fails early. The date of manufacture is usually shown in the serial number (although Bradford White and some Americans and Lochinvars use a letter code where the letter corresponds to a year). Date of installation is better, though, because water heaters can sit in warehouses for years before being sold. In some measure, if you read our service pages, you can get a feel for some of the difficulties that you'll encounter with certain makes and types of water heaters if you decide to service yours.

What: Tank location
Why: So maintenance/service people know where to find it.

What: Gallonage/Btu/Wattage
Why: This is useful for determining whether the tank is sized for the application. Too little heating capacity stresses the tank and annoys tenants through a lack of hot water; too much and you waste money both up front for the tank and over time in greater energy use.

What: Ceiling clearance.
Why: If you're going to service a tank and change the anodes, you'll need to know whether to get standard rods, or segmented ones for low-clearance situations.

What: Condition of combustion chamber in gas heaters.
Why: The roof of the chamber is the bottom of the tank and can give clues to the condition of the heater. A good bottom is one with nothing more than gray metal and a few white condensation marks. Rust or running-water marks, as at right, are bad signs.

A blackened combustion chamber is a sign of serious and dangerous sooting. All this said, you're not going to be able to perform this check everywhere. Few high-recovery water heaters today have a combustion chamber hatch. But they're still common on light commercial tanks. New federal standards may eliminate them altogether. Too bad.

By the way, another place to look for signs of soot is inside the draft diverter and on the cover below it, as in the photo at lower right.

Why do we dwell on sooting? It can become a fume and fire hazard. It means that the flues are not drawing properly. Dirt, lint, diatomaceous earth in pool rooms, can all be sucked into the burner and clog it, and that's the start of soot problems. Keep floors around and under water heaters clean. Or it can be airflow or venting issues that do it.

What: Condition of element ports in electric heaters.
Why: This is where signs of leakage will appear. Also, if leaking water damages the spring clips that hold electric thermostats against the tank, it can compromise the operation of the heater. Care should be taken to put everything back the way it was. The photo at left shows an element port. "Back the way it was" includes insulation!

What: Earthquake strap
Why: It's been code in California since 1992 to strap new and replacement tanks. A proper strap comprises heavy steel bands top and bottom lagged into wall studs, not flimsy plumber's tape screwed into Sheetrock. Although it's not code, we think blocking behind the tank is a good idea, too, if there is any room for movement there.

What: Water pressure.
Why: Pressure that is too high can damage tanks and plumbing. Eighty pounds per square inch is considered the maximum safe level. If you're losing tanks for no apparent reason, consider a test for thermal expansion. This is hard to test for with commercial tanks because you never know when someone will turn on a hot tap somewhere in the building and ruin the test. If that can be dealt with, the test is as simple as attaching a pressure gauge to the drain valve, making the tank fire and watching the movement of the gauge. We have a recording water pressure gauge that reads fluctuations for 24 hours and marks the results on a circular graph in the same way a seismograph does.

What: Plumbing. Is it top-plumbed, or side-plumbed? Where does the piping run? There's usually a cold shutoff valve. Is there a hot one as well? How close are the shutoffs to the surface of the tank? What is the diameter of the piping? Is it steel or copper? Is anything leaking?
Why: Side-plumbed tanks are easier to work on and we encourage them. Shutoffs on both lines make it easier to prevent water from gushing out of upper-story piping while someone is working on the heater. Also it's easier to solder, if that's necessary. On some makes, top-plumbing will have to be cut and resoldered to service the tank. The closeness of the shutoff valves to the tank will determine whether water to the tank can be shut off or if it will be the whole building while you slice off the valves and move them farther back. Piping diameter and metal type will help service people bring the right parts. Leaks are bad news. They can kill a water heater from the outside-in that otherwise wouldn't have failed from inside-out for years. They should be immediately fixed, if possible. "If possible" because if the nipple screwed into the tank is severely corroded and wet, there may be damage to the tank port threads and nothing there may ever seal again.

What: Recirculation pump. Is it running? What make and model is it? Is it valved properly? Is it sized properly?
Why: You'd never know whether a recirc pump was running just by looking at it. A properly functioning pump is whisper-quiet. So is a dead pump. We use a mechanic's stethoscope to check them. It looks like a doctor's except that it has a long probe instead of a medallion on the end. With it, you can hear the whir of the motor. A long screwdriver will also work. If you aren't sure whether you can hear the pump or not, you're probably not hearing it. That said, if the pump is on a timer or has a recirc thermostat, no sound doesn't mean a dead pump. You have to take these other things into consideration. The acid test of pump failure is to go to the far point in the recirc loop and see how long it takes to get hot water. Don't replace anything until you've done that. Oh, and recirc thermostats should be set 20 degrees lower than the tank thermostat. We've rarely found them set right.

Why make and model? So you'll know what to get if it breaks. You can also look it up in a parts book and make sure it's the right pump for the job. Too-powerful a pump and you can scour away the insides of your copper piping and start having leaks.

One other question: is the pump valved for flushing out air if a tank is worked on? If not, there is a chance that the pump will air-lock and burn out when the water pressure comes back on. For a fuller explanation and our thinking on this, visit the recirc page.

What: Temperature/pressure relief valve (T&P). Does it work? Is it properly piped?
Why: T&Ps are installed in every water heater made today and in the gigantic majority of cases, they are totally ignored. They exist to vent if heat and/or pressure exceed certain limits, to keep the tank from exploding. But residential ones are quite prone to failure, especially in hard water, and even commercial ones occasionally fail. Nobody wants to mess with that, so they never test them.

"Is it properly piped?" we ask, because if changing one is easy, you'll be more inclined to test them. And also because in a different sense, if it's not properly piped, it can be a hazard. Code dictates that a drain line of the same diameter as the valve should proceed generally downward to about six inches from the floor, although they are often piped through a wall and outside. If that line makes a few turns and is soldered, then changing a valve involves cutting the line, changing the valve and resoldering the line. The union at right shows one possible alternative to that.

Now, let's backtrack a bit. We mentioned "improperly piped." We frequently encounter T&P drain lines that have been plumbed downward, then back up, usually to make use of an old drain line for a taller tank that runs through a wall. In one case, we saw a T&P that had been screwed in so that it was facing straight up and the drain line was attached so that it ran straight up, then over, then down.

The problem is that if the valve opens and water comes out, it will pool in the valve and corrode it shut. Or water in a low spot might freeze in a colder climate and form a blockage if the valve needed to vent. Whatever, be aware that this is serious business. Water heaters don't blow up every day, but when they do, it's catastrophic and electrics are somewhat more prone to explosion than gas ones.

To test a T&P, pull up on the handle for a few seconds, then release. Water should flow freely, then stop. If it does nothing when you pull the handle, or drips or dribbles when you release it, it needs to be replaced. Drips and dribbles can sometimes be stopped by banging on the pointed hub of the handle with a pair of pliers or other tool.

One more thing: If a T&P is periodically opening, it might well be a sign of dangerous (to the fixtures) pressure and/or thermal expansion and more testing should be done.

What: What is the condition of the vent?
Why: The vent carries poisonous exhaust gases outside. If it has fallen down, or is leaking, then there can be both a fire hazard and an asphyxiation hazard, especially if it's beneath a tenant's apartment.

The photo at right was from one of our early inspections. We've since found something like this at least 20 times and we've lost track of the number of vents we've seen that were in the process of falling. Note the shiny foil connecting the draft diverter and the first vent section below the fallen part. It's tape. Our experience: don't use tape; it's not reliable. Use sheetmetal screws.

Also, draft diverters are designed for specific water heaters. Don't try to mix and match them. In the same way, the vent diameter should match the tank flue diameter. If the vent diameter is smaller than the flue's, backdrafting of gases into the space is sure to result. That, in turn, could result in sooting and a fire hazard.

What: Ventilation screens
Why: They affect proper function of the tank. There has to be sufficient oxygen for gas to burn properly. In some cases, too little and the tank won't stay lit. It's not an issue if the tank is in a large space, such as a basement, but in a small utility room, there needs to be screens with a surface area of one square inch per thousand Btu and they must not be blocked or dirty.

What: Thermostat setting
Why: Make sure it's set to 130 degrees. Legionella bacteria that cause Legionnaire's disease can grow in the bottom of a water heater set to 120. But much above 130 and the risk of scalding increases rapidly. At 150, it's instantaneous. Also, higher temperatures increase energy costs and dramatically increase the amount of sediment a tank produces.