Figure 1. Enamel paint on a residential steam boiler will scorch at about 320 degrees Fahrenheit. Jacket scorching is the first evidence of an overheating event of the boiler block it encapsulates.

Figure 2. When heat-induced oxide discoloration occurs, ferrous metals turn a distinct color if subjected to high tempertures. This discoloration is the result of a chemical change. Ferric and ferrous oxides form at temperatures above 1,600 degrees Fahrenheit. These oxides are initially in the form of a distinct red, and later, a black blue discoloration.

Figure 3. Sludge in a low water cut-off (LWCO) switch is an indication the homeowners have not maintained the device, which can eventually lead to it failing and causing a fire.