How to Apply Boiler Sealer Properly

A leak or crack in your boiler can be fixed with a simple sealer solution. These boiler sealers are designed to be used in steam or hot water boilers. It creates a chemical seal that is tough, expands with heat and resists pressure.

Very similar to products you can purchase for your car, the seal works by mixing with the water in the boiler and creates a gummy seal in any cracks or small holes. The liquid seals are not to be used in systems with water lubricated pumps, or base board radiators. It should also not be used on excessive leaks, as it won’t work on very large cracks or holes.

Step 1: Precautions

Liquid or powder sealant is harmful to breathe in. Try to work in a well ventilated area. If this isn’t possible, be sure to wear a mask to prevent you from inhaling the vapors. Wear gloves and eye protection to prevent the product from getting on your skin or in your eyes. Also be sure to wear clothing to cover your skin. If you do get any of the product on your skin, rinse it immediately with soap and water. The empty containers of sealant need to be disposed of properly, so check with your local regulations on proper disposal methods.

Step 2: Applying the Sealant to a New System

The boiler sealants are available as a premixed solution, or a powder that needs to be mixed prior to application. Most of the powdered sealers only need to be mixed with a little water. Others can be added to the boiler in powder form. Check the directions on the product to find what needs to be done. Both types of products will have complete instructions, be sure to read through and follow them accurately.

For a new boiler, fill the boiler partially with water. Run it with the temperature normally. Remove the safety fitting or valve. Pour one quart of the sealant in the opening. (Some products will recommend two quarts.) Close the opening and fill up the system. Maintain the temperature until the water has circulated. After it has circulated, the cracks should be sealed.

Step 3: Applying to an Existing System

On a steam boiler you will want the boiler to be filled to 1/2-inch above the crack. Find an opening nearest the leak, and pour in the sealant. If there isn’t an opening near the leak, use the safety valve. The directions on the bottle will tell you how much sealant to use. Close the opening and gradually adjust the pressure to the maximum allowance. Until the leak is sealed maintain the same pressure.

Step 4: Contacting a Professional

If you are uncomfortable working with your boiler, a professional can fix leaks and cracks for you. This will be more expensive than doing it yourself, but it may be worth the money depending on your comfort level.

If the leak is large, or the sealer doesn’t work, then it may be time for a new boiler all together.