Why Little Leaks can Ruin and Jeopardize a Big Boiler

But it’s just a little drip… It could be around a hand hole, or maybe somewhere in the boiler system a valve packing is leaking.

The most common leak is a “weeping” relief valve. Many sites have relief valves dripping or leaking, but since they are piped to a drain, they don’t worry much about it, and take the “out of site out of mind” approach.

This is a problem in both hot water and steam boiler systems.
Hot water heating systems are not designed to have much make up water. These systems don’t typically need or get regular water analysis. The loss from any leak must be made up somewhere, and often it is through the automatic fill valve. This make up water is untreated and can be extremely corrosive to the boiler. The fresh water brings in oxygen and minerals that will end up wreaking havoc on your boiler over time.

The minerals will insulate tubes and make hot spots that can warp or fail. The oxygen can make for pitting and tube corrosion. The next thing you know your boiler that should be good for 20-30 years is ready to fail in five.

If a shortened boiler life is all that happens, that’s not bad. Your failure may just be leaks and expensive tube repairs. These same mineral deposits can corrode and seize the relief valve shut. If the relief valve doesn’t work when it’s supposed to, you can have a catastrophic failure (i.e. Explosion).

  • Fix all hot water boiler system leaks in a timely manner, (big or small)
  • Conduct periodic water sampling even from closed systems.
    • Make sure that oxygen and contaminant levels don’t indicate the presence of untreated water in your system.
  • Consider make up water meters
    • We try to design make up water meters into all of the automatic fill systems of hot water boilers. The meter needs to be read and logged. Unusual water use can mean a problem. Certain volumes used over time may mean treatment with oxygen scavengers and dispersants may be needed.
  • Safety relief valve testing
    • Relief valves must be tested regularly. It’s code, its law, and it’s really important. Be careful to do it properly so the valve re-seats and you don’t get hurt. Be mindful of where the discharges are.

Even though they are very simple, when compared to steam boilers, hot water boilers, and their unique issues also need proper care and respect. A small hot water heater killed six kids and took out a substantial part of a school in Oklahoma in 1992 (Star Spencer School disaster). Pressure vessels don’t have to be big to hurt you.


Honeywell Combustion Safety has been in business since 1984. With engineers and staff members that sit on Code committees such as NFPA 56, NFPA 85, NFPA 86, and NFPA 87, our inside expertise is integrated within all of our practices and our global reach ensures that customers around the world are kept safe. Honeywell Combustion Safety offers Testing and Inspections, Engineering & Upgrades/Retrofits, Gas Hazards Management, Training, and Field Services for all industrial facilities and different types of fuel fired equipment. Contact Honeywell Combustion Safety at +1 216.749.2992 or visit www.combustionsafety.com for additional information.


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