Tankless coil leak (C) Daniel FriedmanHeating Boiler Chemicals, Treatments, Leak-Stop
Use of additives & treatments in hydronic & steam boilers

  • CHEMICAL TREATMENTS, BOILER - CONTENTS: description of chemicals & treatments used in hot water boilers, steam boilers, & other heating equipment: boiler water chemistry, corrosion control, leak repair, stop-leak products.
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Heating boiler chemicals, treatments, & leak-stop:

This article describes various chemical additives & treatments used in hot water & steam heating equipment to condition water, prevent corrosion, adjust pH, and to stop boiler leaks. Various chemicals are added to both hot water heating boilers (hydronic systems) and to steam heating boilers to control problems such as corrosion, scale formation, and surging.

We list products & product sources, describe boiler chemical properties, and include links to the products' MSDS information. We also discuss & link to additional heating equipment troubleshooting information such as how to find and fix leaks.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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Heating Boiler Chemical Additives, Treatments, & Stop-Leak Boiler Liquids

Hercules (Oatey) Boiler Liquid stop-leak -

Article Contents

Fix Leaky Baseboards with Additives?

Reader Question: how to repair a pinhole leak in copper baseboard

I'm a journeyman plumber and I know how to braze but I'm not sure how to go about repairing a pinhole leak in a copper hot water baseboard heater. Obviously it has to be dry before I can braze it but how do I drain it and once repaired how do I properly fill it up with water and bleed the excess air?

Reply: solder repairs of small leaks in copper heating baseboard piping

The proper repair of a pinhole leak in copper piping would be soldering not brazing. But you'll most likely need to remove the water from the baseboard heater first. Or one can cut out a bad section of tubing or piping and solder in a short section with unions and copper piping of the same diameter. Be sure to properly sand and prep the copper pipe surfaces, remove any burs, and use a soldering paste or flux to assure a good solder connection.

Watch out: often the presence of a single pinhole leak is an indicator of more trouble ahead. Corrosion, or too-thin or defective copper piping may be prone to developing multiple leaks. I'd go ahead and patch or repair the present leak, but I'd keep an eye on the building heating distribution piping and baseboards for more leaks down the road.

List of common chemicals found in steam boiler water treatment compounds and reference to their MSDS information

Photograph of an open top gravity type storage type steel water tankIndeed some steam heat systems, usually commercial, may contain

For an explanation of pH and its importance see WELL DISINFECTANT pH ADJUSTMENT

Carbonic acid (H2CO3) formation in heating boilers

Carbonic acid (H2CO3) formation in heating boilers and the resultant need for boiler water treatment:

Carbonic acid (H2CO3) build-up in hot water heating systems can occur in areas where the pH of your boiler water is below 8.5 or where other heating system malfunctions cause this inorganic corrosive acid to accumulate in hot water piping.

High carbonic acid, like excessive oxygen levels in heating water, can lead to hot water piping leaks, water damage, and loss of heat in the building. In a steam heating system, condensing steam dissolves carbon dioxide (CO2) to form carbonic acid that in turn corrodes piping.

Ask your heating technician if your boiler water needs treatment or if your system needs additional venting equipment to remove excessive gases from the heating water.

Treatment chemicals for acidic boiler water may include lime and soda ash (COH), phosphate, chelates, oxygen scavengers, neutralizing amines, or filming amines, all designed to protect the heating system boiler and piping from acidic corrosion.

Check with your boiler service company and take a look at the boiler service tag - let me know if any additives were used in your system (unlikely in residential steam boilers) and we can research further by reviewing the MSDS for those products.

Corrosive liquids used in some treatment compounds are skin, lung, and eye irritants (and considered unlikely to be ingested), but you would not expect to find these being released at harmful levels into occupied space from a steam radiator steam leak, since the same steam is also vented quite normally through steam radiator vents during normal system operation.

Use Wetting Agents in Heating Boilers?

Reader Question: use of wetting agents to improve hydronic heating boiler heat transfer efficiency

23 March 2015 Karl R. said:
Have you ever used chemicals to increase the operating efficiency of a hydronic heating : so-called "Water Wetter" products ? These products function by reducing the surface tension and lowering the specific gravity (viscosity) of water....thereby increasing the thermal conductivity and the ability of water to transfer heat to the end radiation method ? If so, were the results every measured and tabulated ?



You ask an interesting question and indeed a literature review (reported at REFERENCES) finds a very large body of research on heat transfer and the effects of deposits of precipitates, corrosion, velocity, turbulence, and additives across a wide range of heat transfer components studied by experts.

Water Wetter such as Red Line's "WaterWetter®" is an automotive cooling system additive used in racing engines [redlineoil dot com] sold at about $12. U.S.D. per 12-ounces and including a corrosion inhibitor (intended to address the corrosion that occurs in aluminum-core automobile radiators) and a wetting agent that improves heat transfer between very hot engine parts such as the automobile engine's cylinder wall and the cooling fluid and cylinder heads and cooling fluid. One bottle treats 3-5 gallons of liquid. (Thus the cost of treatment of the volume of water in a typical heating system would be a bit pricey).

In hydronic heating systems (hot water heating boilers) the operating temperatures are nowhere near that of an automobile engine, and from my reading the properties of heating water flow inside of radiators and baseboards is also different in nature: with great turbulence that improves heat transfer and without the development of laminar flows or cavitation that can reduce heat transfer in an automotive engine. In automobile racing such as dragsters using nitro fuels, still higher temperatures probably make even a small improvement in cooling significant.

Here are excerpts from the company's technical literature that explains how water-wetter works in automotive racing engines.

Water has twice the heat transfer capability when compared to 50% glycol antifreeze/coolant in water. Most passenger automobiles have a cooling system designed to reject sufficient heat under normal operating conditions using a 50/50 glycol solution in water. However, in racing applications, the use of water and WaterWetter® will enable the use of smaller radiator systems, which means less frontal drag, and it will also reduce cylinder head temperatures, even when compared to water alone, which means more spark advance may be used to improve engine torque

... The conventional spark ignition gasoline engine is not a very efficient power plant. A considerable amount of the available fuel energy must be rejected from the metal combustion chamber parts by the coolant and dispersed to the atmosphere through the radiator. This heat rejection is necessary in order to prevent thermal fatigue of the pistons, cylinder walls, and the cylinder head. Another problem is that the combustion chamber must be cooled enough to prevent pre ignition and detonation. The higher the combustion chamber temperatures, the higher the octane number required to prevent pre ignition and detonation. Since the octane of the available fuel is limited, increasing temperatures in the combustion chamber require retarding the spark timing which reduces the peak torque available. Higher inlet temperatures also reduce the density of the fuel/air mixture, reducing available torque further. For these reasons reducing the flow of heat to the coolant usually reduces the efficiency of the engine 

... Red Line WaterWetter® can reduce cooling system temperatures compared to glycol solutions and even plain water. Water has excellent heat transfer properties in its liquid state, but very high surface tension makes it difficult to release water vapor from the metal surface. Under heavy load conditions, much of the heat in the cylinder head is transferred by localized boiling at hot spots, even though the bulk of the cooling solution is below the boiling point. Red Line's unique WaterWetter® reduces the surface tension of water by a factor of two, which means that much smaller vapor bubbles will be formed. Vapor bubbles on the metal surface create an insulating layer which impedes heat transfer. Releasing these vapor bubbles from the metal surface can improve the heat transfer properties in this localized boiling region by as much as 15% ...
- Redline Synthetic Oil Corp. (ret. 2015).

There does not seem to be evidence supporting use of an automotive racing product wetting agent in heating systems and a literature review to date has not (at least yet) found research supporting wetting agents for heat transfer improvement in hydronic heating systems as being as significant or important as other additives addressing foaming or other heat transfer impediments.

Stop Leak Products for Heating Boilers, Piping, Radiators

Reader Question: using Leak-Stop in a Hydronic Heating Boiler: how to fix clogged zone valves & air bleeders

2/4/2014 Ray  said: [originally posted at ZONE VALVES, HEATING]

I have had a small boiler leak, I put a quart of Hercules Sealer in my boiler,It stopped the small leak, now it seams like my zone valves (Automag) are not opening when the zone calls for heat, or maybe my automatic air valves on my baseboard heat trim may be plugged, Should I now drain my system to clean out excess sealer, what do you suggest? \

[Click to enlarge any image]


Ray, I took a look at the Hercules Boiler Liquid described as stop-leak for warnings about clogging of zone valves or circulators and didn't see any warning. It is significant that at least some of the products I reviewed, including Hercules Boiler Liquid explicitly assert that they do not clog heating systems. Quoting:

Seals and repairs cracks and leaks in steam and hot water systems. This liquid formula will not clog hot water coils, controls, valves, or vents. Forms a tough seal that expands and contracts with heat. Resists high pressure and is not affected by boiler cleaners. No odors - no priming - no foaming. Does not contain petroleum distillates.

Compatible with Hercules cryo-tek or other types of propylene glycol-based anti-freeze products, chemical additives and boiler treatment compounds. NSF registered/USDA authorized.

Hercules maintenance and stop-leak products. They are formulated for high performance and developed with both the user and the environment in mind. Hercules "clean and friendly" furnace cement is the latest example of this commitment. Its patented formula is the first and only to meet OSHA's requirement of less than .1% crystalline silica. - retrieved 2/4/14 original source

Watch out: nevertheless a quick search for "boiler leak stopper clogging" will indeed disclose some complaints by HVAC techs and others who cite occasional problems with clogged check valves, boiler drains, and other components following boiler stop-leak products. Typically the complaints I found did not name the product used.

So a clogged zone valve or air bleed valve does not sound out of the question. Indeed once the stop-leak has seated and sealed at the actual leak point you may need to remove and clean or replace valves and other clogged system components. I'm doubtful that simply flushing the system will remove a stop-leak (or other debris or goop) material that has already packed itself into a heating system valve. - search results saved 2/4/14 on file

Steps in Un-Clogging your Stop-Leak Clogged Boiler [suspected cause]

1. If your zone valves have a manual-open position and latch, use that to move the zone valve open - at least you'll have heat, and moving the valve (rarely) might free it up

2. Try (with the heating system cooled down) opening and cleaning a manual air bleeder if that's what you've got; if you've got only the float type air bleeder devices, indeed the bottom opening or float could be stuck. Those are inexpensive devices; I'd remove an old one, allow a small amount of boiler water (ounces) to blow out the mount opening, and install a new one.

3. Depending on where the boiler leak was, is it possible your system is air bound? If so we can point you to diagnosing and fixing that problem.

4. If removal of a boiler component confirms that it was clogged, I would contact the company for advice. But before calling them, review the product use instructions I quote below - it might save some embarrassment.

Hercules Chemical Company, Inc.
111 South Street
Passaic, NJ 07055 USA
(973) 778-5000
TEL 800-221-9330
FAX 800-333-3456

Product instructions for the Hercules boiler liquid you used are quoted from the company's information

For low-pressure steam and hot water boilers including all one or two pipe house-heating systems, vapor and vacuum systems: Make sure water level is below product addition point. Remove safety valve on top of boiler. Pour in Hercules boiler liquid through the safety valve opening. Replace safety valve. Fill boiler with water and allow pressure to go as high as safety valve will permit. Even though the leak stops, keep at normal operating temperature from 24 to 48 hours after all the leaks are stopped. When leaks are severe, it is easier to lower the water below the lowest leak, and pour in Hercules boiler liquid , filling the boiler slowly, and keeping the water extremely hot.

For new heating installations: Partly fill boiler. Fire to normal operating temperature. Remove safety plug or fitting, depending on type of boiler, and pour in to opening 1 to 2 quarts of boiler liquid . Close opening and fill system gradually, maintaining heat until circulation is complete and all leaks have stopped. Note: If leak prevents firing of boiler, pour Boiler Liquid into the boiler at any opening nearest the leak. This should stop leak enough to fire the boiler.

For high-pressure boilers: Have the boiler at working pressure. Pour in boiler liquid through the pump, injector, feed water or any convenient way. This liquid can be diluted with hot water to make it easier to use. The objective is to get the liquid into the boiler the simplest and quickest way. Use one part boiler liquid to 100 to 200 parts water according to the size of the leak.

For hot water heating systems: Drain system until water is below plug at top of boiler. Pour boiler liquid into opening on top of boiler. Replace plug. Refill system slowly, keeping heat above 140°F and making sure all leaks are covered by water.

Continue filling and running system until leaks are sealed. Use 1 quart boiler liquid for each 400-sq. ft. radiation. For large leaks, double the amount. Boiler liquid can be used to repair leaks above the water line by filling the boiler above the leak and holding it for several days. The greater the quantity of boiler liquid used and the hotter the fire, the quicker the leak will stop. 
- Hercules product literature, retrieved 1/4/14, source cited below

Boiler Leak-Stop Product Sources

I list Hercules boiler liquid stop leak first because it's the product used by the reader above and because it's widely available at heating suppliers and from other sources. A common ingredient in many of the boiler stop-leak products listed below is sodium silicate. Some products contain additional or alternative chemicals and sealants.

Watch out: the long term performance of any leak stopping additive (in our OPINION) and even the advisability of its use depend on a number of variables including the size, location and nature of the leak, the materials involved, and other factors. Be sure to read the manufacturer's instructions. A cracked boiler or radiator or similar heating components that bursts can be dangerous and in any event may risk extensive building water damage or even costly mold contamination if the leak is not found and water removed promptly.

Try JB-Weld Epoxy for Cracked Home Heating Radiator Repairs?

Some readers have reported and we consider that it may be possible to repair a small crack or leak in a cast iron radiator using an epoxy product.

One source to consider (we have not tried this) is JB-Weld, a producer of a range of epoxy and sealant products sold most readily in automotive supply stores and some building supply stores.

However if the radiator leak or crack is not in a location at which you can thoroughly clean and prep the surface, we're doubtful about this approach.

For repairing leaks in cisterns  see CAULKS, NONTOXIC or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Hazards of Steam Radiator Leaks

Reader Question: are steam radiator leaks dangerous?

Josh asked: I have an old one pipe steam radiator that has a small crack about 8 inches up. It drips a bit but my concern is the steam. Is this dangerous to have expelled into the air as far as breathing quality. I am not sure If it is a health issue. I have some concerns about having It replaced with a cheap one from china. Thanks so much for your help. - Josh (also by email) J.F. Thank you so much for your help.

R  said: Today at work, a few pipes and radiators blew in some of the rooms. The leak and steam got so bad you could hardly see your hand held out in front of your face. I was in there for a while trying to find the shut off for the water and keeping the water from leaking out into the hall. I was breathing all that steam in for quite some time and I was wondering if there is anything I should be worried about. My lungs and eyes were a little irritated, but I am wondering if there could be something more. - R. 1/30/2014



A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with leaky radiators, including possible hidden damage from prior or long-standing leaks.

That said, here are some things to consider:

Follow-up comment: Harmful chemicals in steam from steam boilers?

Thanks for the quick reply Daniel. I was unsure if chemicals were commonly used in the w

Reply to R about steam radiator leaks & chemical exposure:

While residential and most commercial steam systems operate at very low pressure - under 1 psi, there are some commercial systems that work at higher numbers - where an actual explosion would be potentially dangerous.

I am GUESSING that you are talking about a low pressure steam system and a failure of one or more steam vents on radiators - or an actual burst steam pipe.

The immediate dangers would be steam burns, or if vision is obscured, other obvious hazards like not being able to see to get safely out of the building.

Past those immediate worries, you will want to find out what boiler additive chemicals were being used in the steam system in your building, then to look at the MSDS exposure guidelines for those products. Without that data, an immediate answer to your question would be just speculation.

As I note in the article above,

Check with your boiler service company and take a look at the boiler service tag - let me know if any additives were used in your system (unlikely in residential steam boilers) and we can research further by reviewing the MSDS for those products.

Corrosive liquids used in some treatment compounds are skin, lung, and eye irritants (and considered unlikely to be ingested), but you would not expect to find these being released at harmful levels into occupied space from a steam radiator steam leak, since the same steam is also vented quite normally through steam radiator vents during normal system operation.

Let us know what chemicals were in use and if needed I'll be glad to do some further research.

With any chemical, even distilled water, the poison is in the dose.

Steam Boiler Treatment Chemicals & Boiler Water Color Indicators

Reader Question:

After 23 years I have a question no one knows the answer to.

During thousands of home inspection I put a flashlight behind the boiler sight glass. I do this because someone told me if I saw scintillating particles that could mean the boiler was leaking and that stop leak was in the boiler. I have seen this and reported further evaluation is necessary to determine what the problem is because any leak may reoccur at any time.

Today when I did so the boiler water was phosphorescent (green). Not green all the time like antifreeze just green when light was shining through it. I checked with just about all the home inspectors older than me and all had no clue. I checked with a plumbing contractor and a steam boiler supplier, no one had a clue.

You are my last resource, do you have any ideas? - Anon by private email to DJF 2016/05/04.

[The writer is a professional home inspector in New Jersey.]

Reply: some boiler treatments deliberately color the water to indicate presence of a treatment or to monitor boiler water pH or other chemical attributes

I knew that there are numerous boiler additive & treatment products but I didn't know the answer to the green-tinted boiler water. In response to your interesting question I did a little research. I first suspected that it was an antifreeze or other boiler treatment added and that shows up better under the wavelength of your particular flashlight.

About the interpretation of particles seen in the sight glass, having drained a boiler or two, opened baseboards and radiators, and otherwise made a mess of things, I have never seen boiler water that looked clear and clean.

Steam systems are particularly different from hydronic systems since, as you know, normally the water in a hydronic system is fixed - we don't normally change it nor add to it except in response to a leak or to some service procedure. But as steam systems are always taking in new water (and losing a little through the steam vents before they close down), there is an accumulation of mineral levels as well as other crud - fomenting an entire industry of steam boiler treatments and additives to control scale and corrosivity.

When the steam boiler is in heavy operation you're likely to see suspended rust particles in the water.
When the steam boiler has been off for a time much of the suspended solids, certainly the larger ones, settle out and the sight glass will clear up.

I don't usually see antifreeze in a steam boiler as the anti-freeze - treated water is going to be consumed and as one steam boiler thread put it, makes for "expensive boiler water". But I might see a tech put antifreeze even into a steam system to protect from freezing if for some reason the heat is being left off but the boiler is being drained. (That'd be an odd procedure.)

Other more common steam boiler treatments for corrosivity or scale or pH can impart a green color or a pink color. You won't always see it. Usually these colors are deliberate and are indicators to the boiler maintenance operator that adjustment or treatment is needed. This is an old concept discussed in boiler texts like Heselton:

Here is an excerpt from Heselton's Boiler Operators' Handbook found by Google-search

If you're color blind make sure the boss knows it and sees to it that the chemical consultant provides a test ... Steam boiler water should have the highest value ... You add acid until the yellow turns pink or the green turns purple. - Heselton (2005)

Here is why you won't always notice the color or tint imposed on the steam boiler water by treatments & additives

1. it may not be present

2. it may be present but obscured by floating solids.
When the boiler water has cleared up of heavy suspended solids, and where the additive is a PurePro product or a RectorSeal product, some of these can leave a greenish tint to the water. Other pH-sensitive chemical additives (BW-408PD from Canon Water Technology) can turn the boiler water pink to indicate its presence.

3. It may be present but chemically exhausted and in need of replenishment.

Here is an excerpt from a RectorSeal article on boiler additives that can give a green tint to steam boiler water:

One of the most notable benefits of water treatments is the color indicators manufacturers build into them, which are useful for visual water-quality checks. After application, a pinkish purple water sample indicates a proper pH water chemistry of approximately 8.2, which is neither too alkaline nor acidic. Blue or bluish-green water indicates more water treatment is needed. A complete flushing may be needed if subsequent applications do not generate the proper water color. Too much alkalinity can cause surging, scale buildup, or eventually “caustic embrittlement,” a process that causes the metal to crack. Too much acidity, on the other hand, leads to corrosion. - Grodjesk (2012)

I'll also provide both Grodjesk's article and a Lenntech article that gives a nice synopsis of the boiler scale problem.

There are other sources of green or blue-green tints in water: soluble iron salts (green), or copper (blue-green) for example. So I suppose that very corrosive boiler water might also produce a tint seen in the sight glass. If that were the cause, IMO that'd be a warning that further investigation is needed as the boiler water may be corrosive, risking costly heating system damage or even loss of heat.

In sum, I would be careful what I'd say about boiler water color. Warning that something's wrong (corrosive water, dissolved copper) when actually something's right: the boiler has been treated properly and the additive deliberately imparts a tint to the water.

And I'd be careful what I'd say about the meaning of suspended particles in the boiler water. A lot of debris may indicate any of several problems: lack of needed treatment, scale formation, biological formation, or even surging. And high debris level risks clogging an automagic water feeder, TPR valve, or other controls. But as the sight glass is not usually crystal clear, I'm not sure where to go with the observation.

As my admirable friend Mark Cramer (ASHI Tampa) says, ".... it depends."

Watch out: On the other hand, if the water level is low in the sight glass that's a serious warning, and if water is not visible in the sight glass (and the sight glass valves are open so that water should be visible) the system is unsafe and should be shut down.

Watch out: a backflow preventer is always recommended on heating boilers, both hydronic and steam systems. Boiler water can be pretty nasty, and where additives and treatments or antifreeze are in use, it could be toxic or even fatal if consumed by accident. See BACKFLOW PREVENTER VALVE, HEATING SYS for details.

Let me know if this does the trick, and thanks for asking.

Research on color agents in boiler treatments


Continue reading at BOILER LEAKS CORROSION STAINS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ANTIFREEZE for BOILERS - when, where, how & why to add antifreeze to a heating boiler

Or see BACKFLOW PREVENTER VALVE, HEATING SYS - extra important where toxic chemical additives are in the boiler but always recommended

Or see CONDENSATE RETURN PIPES, PUMPS, STEAM where leaks and boiler leak-stop additives are cited

Or see LEAKS at BASEBOARD, CONVECTOR, RADIATOR where use of additives to try to stop radiator or baseboard leaks is described


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