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Plumbing in the Home/leak in a gas fired steam boiler


QUESTION: I know I will eventually need to replace my gas fired steam boiler - again - but right now I do not have thousands of dollars to put out for that. By the end of last winter I was constantly refilling the boiler. It had a leak above the water line that let steam escape into the basement while it was firing. I have read about sealants that can be added to the water to seal off leaks. Do they work as a stop gap repair until I can replace it? IS one type or brand better than another?

No knowing the size of your boiler or cause of the leak, It would be risky recommending any product to repair this leak. Most of the leak stop products are for very minor cracks and do not do well for leaks caused by corrosion.  Steam boilers operate at higher temps and pressures can change dramatically and very quickly. My recommendation is to to remove the jacket and locate the leak. If it is a crack in the heat exchanger then perhaps one of Hercules' products will  seal it. If it is due to corrosion #usually in the push nipples that connect the sections together# then you may be able to rebuild it.
when adding boiler leak liquid to any system, you run the risk of causing other problems that may effect the controls, the gages and other vital components to your system. Get a professional to look at it once you have located the leak.
Also, you are doing  more damage to your system by constantly adding fresh water. What this does is introduce minerals and dissolved solids that boil out and are settling at the bottom of the boiler. Eventually, when the boiler fires it will sound like a percolator and transmit the noise through the building, not to mention, decrease efficiency.
Being a fellow New Yorker, my advise it to get it looked at now, winter is right around the corner.

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QUESTION: I dont disagree with you however I had a plumber out to change the pigtail last season and he simply said - "It's shot". So I know these guys all want to replace it and make some $$. Unfortunately I cannot afford to replace it right now. I may have to just give the sealant a shot.

What about some sort of heat resistant sealer or cement that I could apply directly to the leaking area and not introduce into the whole system?

BTW - NJ not NY.


ANSWER: If you can Identify the size and location of the leak, then you will be able to determine if and which product you can use. A small hairline crack will be repaired using Hercules boiler liquid. A gapping hole  or corroded nipple and it won't work. Any type of sealer or epoxy  that I know of is not flexible enough to withstand expansion and contraction of the metal exchanger. Welding cast iron is really tricky but not impossible.
There is a product call Blue magic Quickseal High temp paste that I have heard about but never used. It might be worth a shot

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QUESTION: I took your suggestion and found some high temp epoxy to patch a couple of holes that were allowing steam to visibly leak into the basement from the boiler. I can hear that there are other leaks above the water line that are allowing steam to exit up the flue. I did not see them when I had the jacket off. They must be on the top covered by the sheetmetal from the exhaust. Would it be safe/advisable to try and remove the sheet metal to repair those leaks or is that too risky? I did add some of the HErcules Boiler liquid but I do not think I did it properly. I ran the boiler at normal water level thinking the steam would find the leaks but I now think the product intends you to overfill so that the hot water/boiler liquid solution reaches the level of the leak. Does that sound correct?

According to the directions I interpret them to mean that the refill should be up to the highest leak point. In your case the top so yes I would over fill and fire boiler as directed. Based on your descriptive I would have to agree with your plumbers assessment.
As a side note , your utility company may be able to help you with replacement cost with their upgrade/efficiency programs. It won't hurt to ask them  if they have such a program.

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Jay Nicholas


Plumbing & Heating (warm air, hot water & steam heat)


40 years in the business, 35 years as a lic. master plumber in NY State. Retired

Graduated Magna cum laude at the School of Hard Knocks

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Commercial, residential and light industrial. You name it ...I have probably worked on it

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