can you weld a pinhole in a water tank?

I have a 10 year old hydronic heating system in my home. There is a boiler and it leads to a special tank which holds the heated water, which is circulated on demand through wall registers. The thing that makes this tank special is that it also holds potable water, i.e. a hot water tank. The heating and potable water never mix, ever.

My tank has developed a pinhole leak right up on the domed top. I cannot imagine that there wasn't a manufacturing defect, but the warranty says that if the house is sold the warranty ends at 5 years. Before I buy a new tank at a whopping $1200, I want to at least try to fix the pinhole. My heating system guy shook his head and said "it would never hold" but I don't see how I have much to lose. There is almost certainly some kind of liner which I'd have to worry about, so I'd want to use minimum heat.

Anyone have any idea how something like this might be patched? I was thinking of trying a soft solder perhaps.


Reply to
Grant Erwin
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Depending on how hot this gets, you might be able to epoxy it. What is the tank made of? Galvanized steel? You have to get the area near the repair dry on the inside to get it hot enough to solder. It may be very difficult to get the 10-year old surface clean enough to solder well. Make sure there is no trapped water in the tank, or you could have a deadly steam explosion.


Reply to
Jon Elson

Grant, It sounds like Jon has the ticket! Rough up (clean) the outside well and apply a patch over the hole with JB Weld.

Bob Sw>> I have a 10 year old hydronic heating system in my home. There is a

Reply to
Robert Swinney

How thick is the tank wall? You might be able to drill and tap for a small pipe plug like 1/16" NPT.

Reply to
John Kunkel

I would get some JBFix, a small square of metal window screen, and make a 2 x 2" patch.

My experience with these is that they corrode from the inside. If you were to cut this open, you would see corrosion marks. This was so with several aluminum hot water heater units people brought me out of motorhomes. They had a pinhole, and not enough metal that was thick enough to weld to. It just blew holes. Finally, we did the JBFix thing, and they lasted a little while longer, but just until the next cancer popped through at another place.

It's just like freeze plugs. You ever change a freeze plug in a motor block. I did it once, and replaced only the one that was leaking. After firing it up, a week later, another started leaking, as they were all the same age, and all in the same state of corrosion. So, I pulled the engine AGAIN, and did all the plugs. A lesson.

This is not to say that you might patch this tank, and see another ten years of problem free use.

I have had some incredible results with JB products when it was the last best thing to do before replacement. And, for a few bucks, you could do several patches.

Just drain to make sure it's dry, and clean the surface and sand it a bit.

Let us know what you do and how it works.


Reply to
Steve B

One question that's critical: What's the maximum expected pressure of the tank? Is it ever expected that the holding tank will exceed about

40-60 PSI (Typical potable water system pressure), or is it a case of "The boiler doesn't actually boil anything - just makes the water hot, and a pump puts it into the tank at a few PSI/circulates it"?

If it's just "There's hot water inside", then I'd expect it to be no big deal to drill directly through the leak, then sink an appropriately sized stainless steel self-tapping screw through a rubber grommet. No muss, no fuss, no bother.

On the other hand, if the boiler truly is a boiler, then it's probably a pressure-rated system, and as such, things get *REAL* dicey, from both a legal and safety standpoint, no matter how you attempt the fix. If this is the case, it will likely end up being easier/cheaper/safer to just replace the tank, regardless of how bad it hurts the wallet - Better to spring for the $1200 than have the thing fail under pressure and blow the house off the foundation, doncha know...

Pressure vessels are definitely nothing to mess with if you don't know

*EXACTLY* how to do it right, and I wouldn't be surprised if doing anything to it without proper "powers that be" approval, inspection, maybe even a license, etc. etc. etc., could set you up for some *SERIOUS* legal/insurance trouble sometime down the road.
Reply to
Don Bruder

Chances are that the pinhole is a rust through. If you fix one you will probably develop more soon.

Gary Pewitt N9ZSV Sturgeon's Law "Ninety per cent of everything is crap"

Reply to
Gary Pewitt

I think you're actually referring to an indirect fired domestic hot water system.

The "boiler" normally feeds your hydronic baseboards directly with a circulator pump and zone valves if needed. You DHW normally is provided one of three different ways, in-boiler tankless DHW coil, separate standalone water heater with it's own burner, of indirect fired DHW from a separate heat exchanger tank.

The indirect fired DHW normally has a separate heavily insulated storage tank with a heat exchanger coil in it. This heat exchanger coil is normally plumbed to the boiler as an additional zone and there is a separate thermostat for the DHW tank. It's rather the opposite of the in-boiler tankless DHW setup where the DHW is in a heat exchanger coil in the boiler tank.

If this is the case, the tank itself holds the potable DHW water so anything you use to patch it must be potable water safe. The actual DHW tank temperature normally should not exceed 130 degrees and your normal domestic water pressure. The problem is that if the cause of the leak is general corrosion as opposed to one defective spot, you could have the heat exchanger coil ready to go as well and the potential for cross contamination. If you have antifreeze in the boiler side of the system this would be particularly bad.

I think you need to lookup the exact brand / model tank and determine exactly what you are dealing with before proceeding.

Pete C.

Reply to
Pete C.

It isn't a pressure vessel, city water pressure (60-70 psi) is it.


Reply to
Grant Erwin

Poke the tip of an ice pick into the leak, and wiggle it. If the metal crumbles away and the hole gets bigger easily, forget trying to repair it. Corrosion has eaten away a lot of metal, and you are just seeing the spot that happened to go through first.

If it feels really solid, your idea that there might have been a defect could be right. Then the idea of drilling and tapping, or using a self-tapping screw, or epoxy will probably work.

If you decide to try soldering, someone warned about the possibility of pressure buildup leading to an explosion. Of course, you will want to lower the water level so you're not trying to solder with water in contact with the spot. If you lower the water level, it is extremely unlikely that you could build up steam pressure inside the tank by heating one spot. Just to be on the safe side, open a valve so pressure is relieved.

Another idea would be to braze a pipe coupling to the outside of the tank over the leak, and screw in a plug.

Reply to
Leo Lichtman

I would agree - but if I was fixing it I'd braze it with the O/A torch and the "blue" brazing rod. I'd drain the tank down and open it to atmospheric pressure, sand the area around the pinhole perfectly clean, and flow brass on in an area about the size of a quarter or half-dollar.

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Reply to
clare at

Use a self tapping screw and JB weld. Clean area real good .Rough the surface. Tap hole. Apply a generous load of JB and insert screw. Apply excess over the top of everything to seal it up for good.

Reply to

With a self tapper there is always the possibility of setting up a galvanic cell inside, and speeding up the corrosion. I'd go for mesh and epoxy outside (where the epoxy also keeps oxygenated water off the mesh, so that even if there is a dissimilar metal pair connected, there's no oxygen).

Reply to

My experience from seeing the inside of a few dead aluminum hot water tanks is that there is always corrosion in other areas, just waiting to be the next leak. They are like looking at the surface of the moon, little patches of flat craters, being dish shaped. To merely drill in the center and epoxy WOULD solve the problem temporarily in that area, but putting a patch larger than that outside makes the area you are building up a lot bigger, so that it is over the "crater" on the inside. If it corrodes more in that thin spot in the center of the crater, it will just come out where the epoxy is. And if you are drilling into the thinnest part of the crater, you won't have much "meat" to anchor to.

Now, I know this is not an aluminum hot water tank. I do not know what this material is, and if, when it is dead, if you looked inside, exactly what the post mortem examination would reveal. The best way to understand what happened and what the best fix would be is to do a post mortem, but that is what the OP is trying to avoid for as long as possible.

However, once the tank does give up the ghost, cut it up. Examine the interior. See what's there, and what might be the best thing to do in the NEXT case. Also, you can do some tear apart of the actual repairs and see how they performed. There will be a lot of information and things to be learned there, so don't just chuck it without examining. Maybe a sheet of fiberglass with two element fiberglass dope would have worked better.

Anyway, that is what I would do. YMMV. I consider it a good day if I have learned something new.


Reply to
Steve B

I'd clean it real good, and sweat a copper penny onto it. No, really, I've done it before. Good luck,


Reply to
Bob Meyer
1.It sounds like an indirect water heater, and doesn't heat your radiators.

  1. They are usually coated steel, (porcelain), any welding will further damage the coating. What brand is this unit? How old is it?

  2. As others have mentioned, fix one spot and you'll play little Dutch boy with more leaks.

  1. If the whole thing goes while your away you'll flood your basement. Consider this a free warning

  2. Next time replace the zinc anode inside the tank every 10 years or so, if it is accessible.


Reply to

If it's a lined tank you are probably going to have to stick with non-heat methods - the lining can be "Glass" (porcelain) or some sort of epoxy or blown-in-place polyethylene. Either way, the application of welding or soldering heat is going to be a problem.

And consider what will happen if that patch pops big-time, and you have a half-inch gusher flowing your water main full out into the room

- is this tank somewhere you'll have huge water damage problems?

I'd try an external epoxy patch as a stop-gap to either buy a few weeks or get through this winter, and I'd try to work some epoxy inside the hole to act as a mushroom plug of sorts. If it's a flexible lining you could use a mechanical seal like the 'boiler patch bolt' with a big neoprene washer under the head. But if it's a rigid lining (porcelain) you could crack a big chunk off on the inside and accelerate the deterioration.

And now the "r.c.m Monster Garage" question: Is it possible to split up the systems and save a lot of dough in the long run?

Instead of spending $1,200 for that special heat-exchanger tank you install a plain old electric DHW water heater for $300, and a plain hot-water storage tank (or a second electric water heater) for the boiler for roughly the same, and an external water-water heat exchanger and a pair of wet-rotor circulation pumps to heat the DHW from the boiler side.

You leave the electric heating elements turned off for normal use, and if the boiler or the heat exchanger dies, you can fire up the electric elements as an "Oh, Sh*t" backup heat system.

The storage tanks they sell for solar systems are nothing more than an electric water heater with no wiring, elements or thermostats installed. You can even remove the access hatches and see the plugs in the element holes.

There are other dodges to this, but what fuels do you have available at the house?

If you have natural gas or propane available, substitute the appropriate gas water heaters for the storage tanks. (And plug off the vent flues when not in use to prevent heat loss.) And then you have the option to switch over if fuel oil prices spike higher than propane or natural gas, or vice versa.

This is where having a 'Plan B' shines. I have accounts with big condo buildings with two or three Raypak gas fired hot-water boilers for DHW in a tankless pipe-circulation system, one of the buildings has them all in the same room - but plumbed as totally separate systems. No "Oh Sh*t" valves to tie two sections together for a few days in case one of the boilers fails. The hot water might get lukewarm during the "morning rush" but if the residents know, they can adjust.


Reply to
Bruce L. Bergman

Lots of great advice. This problem is greatly compounded by the fact that the shutoff valve which feeds cold potable water to this tank is malfunctioning and will *not* shut off. It's a gate valve and it's just plain stuck.

More details: I was wrong, this tank does not store heating water, only potable water. It has a heat exchanger in it, so boiler water is circulated through the heat exchanger and the rest of the water is potable water. This is good news because when I figured this out at least I could turn my heat back on.

I also have an electric hot water tank and I could have hot water again if the shutoff valve were working. It's soldered inline onto 1" copper pipe, and it's going to be a bitch to fix it. The two hot water tanks are plumbed in series and the electric one is upstream of the boiler-heated one so if I keep the electric one shut off then I can drain the boiler-heated one.

So I decided to try patching the leak. First, I took an awl and gently poked at the pinhole leak. Remember, this tank contains hot water under approx. 70 psi. Well, what happened was that the pinhole rapidly opened up and I got sprayed with hot rusty water, along with my ceiling, etc. The thing that really turned it into a cluster fuck was that the floor drain was plugged with concrete, the bastards must never have tested it. I was able to chip through it and clear the J-pipe in the floor and squeegee the water down the floor drain, and the pools remaining I sucked up with the shop vac, which has seen a lot of duty tonight, more to come.

Anyway, I tried high temperature RTV in conjunction with a sheet metal screw, let it set up for a couple of hours, no way at all did it hold. Next I cut out a patch of copper sheet about the size of a 50 cent piece and had a go at sweating it on using plumber's solder. That's where I am now. Next step is to go cut the water back on and see if it leaks through my patch. If so, off comes the patch and I'll try directly brazing up the hole using bronze brazing rod and blue flux.

I know this patch won't hold for long, I'm just trying to get through the holiday weekend with 4 teenagers here without having no hot water.


Bruce L. Bergman wrote:

Reply to
Grant Erwin

OK, the copper patch didn't sweat on fully. I took it off, wirebrushed the area, and brazed a patch just using bronze rod and blue flux as someone recommended, not that I have any other brazing rod or flux. This patch is holding up, although I'm positive I didn't do the plastic lining of the tank any good. Score another one for the O/A torch. Now my heat's back on and I have hot water. I'll get to replacing the tank when the plumbing supply store opens on Monday, busted shutoff valve too. Thanks to everyone, just tons and tons of great advice.


Grant Erw> Lots of great advice. This problem is greatly compounded by the fact

Reply to
Grant Erwin

The pinhole is only the external manifestation of significant metal loss inside the tank. In other words, It prolly ain't fixable! I had a

10,000 gal. tank that I rehabilitated myself. It took 450 lb. of rod to build up the thinned out sections to a usable thickness but I was dealing with 3/8" plate. A pressure rated tank will need to be recertified under the ASME boiler code. Better to replace the tank with a lined pressure tank available from a well supply co. Bugs
Reply to

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