What you’ll find on this page: Commercial water heater service varies with the kind of water heater it is and how it is installed. Here you can get an idea of what is involved and what issues you might encounter with different brands and configurations.

Commercial Water Heaters and Boiler Storage Tanks

Economies from service here are even greater than with residential tanks because commercial water heaters servicing multiple housing units cost so much more to buy and install. Cost of servicing them runs from 10 to 30 percent of the cost of replacement. Aside from the up-front cost, maintenance can ensure continuity of service, happy tenants and less stress on the staff from the unpleasantly unexpected.

There are many models, and their construction and installation will determine cost and difficulty of service. Some have one anode and one flue. Others have a forest of flues and several anodes. And some have no flues: they’re electric. Such things influence how each type should be serviced.

Boiler storage tanks also have anodes that should be checked and changed periodically. We’ve found that, because of the fewer stresses on the tank, intervention here can come much later than with a water heater, with economical results.

The strategies required for service vary with the unit. You’ll find the following topics treated in detail here:

  • Boiler Storage Tanks
  • Light Commercial Gas
  • Electric Heaters
  • High-Recovery Gas

There’s one thing that all these configurations have in common, so we mention it here. If there is a recirculation line and pump — very common on multi-unit systems, then it’s important to properly valve the system for flushing. We’ve made a separate recirc page to demonstrate the proper setup, with a diagram and examples.

Boiler Storage Tanks

Service here means just one thing: changing anode rods. In our experience, 120-gallon tanks have one or two 3/4-inch anodes that are screwed into the top. Often their hex heads are exposed, but it might be necessary to cut the sheetmetal cover and hunt for them. The boiler and water need to be shut down first, of course. An anode extractor can sometimes be used if there is a central outlet pipe to brace against.

200-gallon tanks typically have 1-inch or larger anodes, often screwed horizontally into the tank at either end. Usually there’s nothing to brace against, even if you can use an anode extractor and brute force is required. Anodes should be replaced when there is six inches of exposed core wire.

Ordinarily, with water heaters, if you pull out an anode and there’s nothing left but the plug, it’s unlikely that a new anode will save the tank, or at best, you’re going to be replacing them every year, which is marginally economical or not at all. But we’ve found that with storage tanks, you can get several years out of the next anode.

As with all systems with recirc pumps, make sure and flush the air from the recirc line when finished or there’s a good chance the pump will air-lock and burn out.

Light Commercial Gas

Usually, these heaters have one or two anodes and one-inch plumbing. On commercial-rated tanks, there ought to be a cleanout hatch, but we’ve seen residential-rated tanks, without the hatch, in commercial situations, even though doing that often voids their warranty — if the factory finds out.

For tanks without a cleanout hatch, the only way to get rid of sediment is with a Muck-Vac water heater vacuum, but that requires two ports on top of the heater — one to vacuum through and the other to return the water after the sediment has been filtered from it. If a tank is side-plumbed, but without a cleanout hatch, it will be impossible to remove sediment buildup unless you disconnect the side-plumbing and use a shop-vac.

Anyway, for other configurations, service involves changing the anode(s) and removing sediment, either by vacuuming or from the cleanout hatch. The latter can be done by hand, with a shop vac, or a Muck-Vac with special attachment.

How often everything should be done depends on how hard the water is and how fast anodes are consumed. However, we think it’s wise to check every tank just a little before it comes out of warranty, especially 75-gallon tanks with one anode. The reason before the end of warranty is this: if the tank should be leaking and about to break, you may be able to get a replacement under warranty. As to the 75-gallon tanks, the reason is that the anode has a lot of interior surface space to protect and thus potentially can be consumed more rapidly.

As with all systems with recirc pumps, make sure and flush the air from the recirc line when finished or there’s a good chance the pump will air-lock and burn out.

Electric Heaters

The first thing to do is turn off the power, then the water pressure. Anodes may be visible on top of the heater, or it might be necessary to cut into the cover to find them. In some cases, they’re embedded in foam insulation, which must be chipped out to get access.

We’ve tried cleaning electric tanks with the Muck-Vac and think that the cleanout hatch is the better choice, either with a shop vac or the Muck-Vac and side attachment. The electric elements get in the way of effective vacuuming. But sediment removal is important, since it can burn out lower elements.

As with all systems with recirc pumps, make sure and flush the air from the recirc line when finished or there’s a good chance the pump will air-lock and burn out. And remember to turn the power back on.

High-Recovery Gas

We saved the messiest for last. Because of their construction, servicing commercial heaters requires more work, time and consideration than the other categories. Cleanout hatches can be used to remove sediment, but the numerous flues on this type of tank limit that method’s effectiveness.

Since access to the anode rods is required anyway, vacuuming is superior, since the Muck-Vac wand can slip behind and between flues and the three to five anode ports provide access to most of the tank bottom.

We suggest that you also look at our section on installation, since many of those tips are designed to make service quicker and more economical.

How often everything should be done depends on how hard the water is and how fast anodes are consumed. However, we think it’s wise to check every tank just a little before it comes out of warranty. The reason before the end of warranty is this: if the tank should be leaking and about to break, you may be able to get a replacement under warranty. Also, check out the section about inspections. That should be done before jumping in and servicing a tank.

Now we’re going to walk you through what’s involved in servicing a commercial heater. We’ll discuss some of the potential difficulties as we go.

Marks on cover so it can be put back correctly after service

The first step is to turn off the water pressure — and make sure it’s really off. There is nothing more disheartening than having water fountain out of the top of the tank and thoroughly drench the electronic ignition. You’ll have a terrible time getting the tank to fire afterward and you won’t dare walk away until you can.

So how do you tell? If convenient, you open a hot tap anywhere in the building to see if any water can still flow. You can also hook up a hose to the drain valve or open the temperature/pressure relief valve.

But it’s also not a bad idea, if in any doubt, to remove the drain valve, in case sediment has plugged it shut or the T&P is faulty. If it’s a ball valve, you can just ram a screwdriver through it to clear it.

Next you mark the tank and cover with a marker pen, as in the photo above. That will make it easier to line up the cover with its screw holes when you’re putting everything back together. There will be four to six screws holding the cover on. Those come out, then you pry the cover upward with a couple of flat-bladed screwdrivers.

Meanwhile, though, you’re also removing the draft diverter and likely a section of the vent, also held with screws or tape, and disconnecting the automatic flue damper. It is usually screwed onto the tank and there is a wired connector that unplugs. Once unscrewed, the assembly lifts off the cover and out of the vent.

We are very fond of side-plumbed tanks. With side-plumbed, no matter what brand it is, access to anodes is quick and straightforward and water can be added to the tank for vacuuming, if necessary, just by opening the cold valve. Also, if connections leak, they’re more likely to leak onto the floor rather than onto the tank.

Composite of outer and inner covers of commercial heater during service

Very many water heaters are top-plumbed. Unless you intend to tear all that out and go to side-plumbed, here are the scenarios you might expect.

What we’re about to tell you is based on our experiences. You might well encounter something different because the manufacturers occasionally change models and create new configurations. That said, the easiest top-plumbed tanks we’ve encountered have been American Standard, American brand and some (but not all) Bradford Whites. Why?

High-recovery gas commercial water heaters have numerous flues to enable rapid transfer of heat. On such tanks, there is an outer cover and an inner one. The inner cover gathers exhaust gases from all the flues to the central vent. The outer cover is just part of the shell. Both are shown in the above-right photo. The black piece is the outer cover, the silver piece the inner one.

Where the plumbing lies has everything to do with ease of service for top-plumbed tanks. That’s because, if the plumbing lies outside the circle of the inner cover, as in the lower photos, from an American Standard heater, then the outer cover can be cut without any danger to anyone (naturally, if your local codes forbid this, don’t do it). You can see where we did this using a saw in the upper photo. The piping passed through the cover at the part marked by the red circles and we simply sliced a U-shaped piece out of each side to take off the cover without having to cut the plumbing.

On every A.O. Smith and Rheem that we’ve seen so far, and some Bradford Whites, the inner cover is the same diameter as the outer one and the pipes pass through both. If such an inner cover were notched out, it would permit poisonous gases to escape into the space around the water heater — a dangerous situation.

For those configurations of tanks, it’s necessary to cut the plumbing to get access and later put on new unions or stainless steel flex lines.

Once the cover is off, on either side-plumbed or top-plumbed, it’s simply a matter of taking out the anodes, inspecting them, and replacing them, if necessary. The rule of thumb is to replace when six inches of core wire are exposed. A secondary rule, though, it to replace them if they’re passivated. That means they’ve sort of gone to sleep for reasons that nobody seems too sure of. If you pull them and there’s no corrosion at all, just smoothness, they’re probably passivated. Putting in new ones might get the proper reaction started. If the anodes are bare wire or just plugs, then there’s a good chance the tank is going to fail soon, or that you’ll have to come back every year to change anodes. Then you have to weigh the cost of that against a new tank.

Another thing to remember. If you remove the covers and you find water inside, or wet insulation, and no apparent cause, such as condensation or a leaking union, then there is a chance the tank is failing. You can feel different parts of the external jacket with your hand. It should be cool. If you find a hot spot, that is an indication that water is leaking there and soaking the insulation. If so, you might want to halt service and put everything back together.

In the middle photo above, two of the anodes were next to the piping. the other two were under the inner cover, which is why we removed it. That involved undoing two screws and pulling the whole piece out. Some are merely caulked to the tank.

Every brand we’re acquainted with except State uses three to five 3/4-inch anodes, requiring a 1 1/16-inch socket. State invariably uses two one-inch commercial anodes that take a 1 5/16-inch socket. Unless you own an anode extractor based on a torque multiplier and shown in the middle photo, or an impact wrench, you remove these as best you can. If you have trouble, tapping the hex head with a hammer sometimes helps. We discourage the use of lubricants, as those could seep into the water that people wash with and even drink.

Even if you have an impact wrench, we suggest loosening only. One of those fountaining incidents we mentioned occurred when someone was using one and took the anode out so fast that he didn’t realize the pressure wasn’t off. When it’s done more slowly, water seeping out from under the nut is a warning sign that all is not right and you can stop before you drench everything. Likewise, when you put the anode back, you’re less likely to cross-thread it.


If you have a Muck-Vac, you can vacuum through the anode ports, moving from port to port to work the entire tank bottom. Once that’s done, it’s time to put the anodes back in, using six wraps of pipe-thread seal tape. If this is one of the configurations where the plumbing didn’t have to be disconnected, this is a good time to turn on the water pressure and make sure all the anodes have sealed in their ports.

Caulking the inner cover of a commercial water heater

Then comes the inner cover, which you’ll want to seal with high-temperature-resistant silicon, as at left. That’s to keep poisonous fumes from seeping into spaces where they don’t belong.

It serves a secondary purpose, too. We occasionally have found where gaps allowed hot gases to spill out around the cold nipple, causing acid condensation and rusting the nipple.

Some covers might not require caulking. We recently saw a Bradford White where the cover slid over a lip circling the heater and didn’t require caulking. Rule of thumb: if the factory caulked it, you should, too.

After that, you just go back the way you came: inner cover, outer cover, automatic flue damper, draft diverter, vent. As to the vent and draft diverter, always use three screws per section, even if it wasn’t that way before. We don’t trust slip connections and we don’t trust tape, even duct tape. We’ve seen too many fallen vents or falling vents and these are highly hazardous to tenant health.

If you’ve cut the plumbing, you’ll have to solder on new unions or male adapters and stainless steel flex lines. We aren’t crazy about any of these, since anything can leak and everything does leak if you don’t go back six months later and tighten it, but stainless steel at least can later be disconnected and reconnected and we’ve had dismal experiences with dielectric unions.

We’ve seen plumbers achieve success with screwing brass, but not dielectric, unions onto plastic-lined nipples (in fact, our sample tank above was done that way) and even with screwing a copper fitting onto such a nipple, but we also saw a slew of instances of the latter, during an inspection, where the copper reacted electrolytically with the steel and caused steady leaks onto a bunch of expensive high-recovery heaters — which can wreck them. Whatever technique you choose — and that includes side-plumbing — keep an eye on it. That’s the only way to keep the water heater gremlins at bay.

When everything is back together, make sure and flush the air from the recirc line or there’s a good chance the pump will air-lock and burn out.

Servicing high-recovery heaters is often an adventure where the unexpected can occur. It’s well to have a large array of tools and parts and Fortune smiling on you. If she’s not, the tools will come in handy. But these heaters can be serviced and made to last many years beyond their normal lives. And their owners can save a lot of money and grief in the process.

Water Heater Rescue

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