Which of the following is an advantage of cast iron boilers?

Cast iron boilers are well-known for their resistance to corrosion, which is indeed a significant advantage. This characteristic arises from the nature of cast iron itself; it has a protective oxide layer that forms on its surface, helping to prevent rust and other forms of corrosion when exposed to water and various chemicals commonly found in heating systems. This resistance not only extends the lifespan of the boiler but also reduces the need for frequent maintenance and replacement, making cast iron a cost-effective and reliable choice for many heating applications.

When evaluating the other choices, unlimited operating pressures are inaccurate as cast iron boilers have specific limits on their operating pressure, which depends on their design and construction. Reduced vibration due to heavy foundations can be a factor influenced by construction and installation practices rather than an inherent advantage of cast iron itself. High brittleness is not typically regarded as an advantage; rather, it can be a disadvantage since brittleness makes materials more susceptible to cracking under stress or impact. Thus, the notable resistance to corrosion stands out as a primary benefit of cast iron boilers.