Hot-water boiler failures are commonly caused by oxygen corrosion, deposition, corrosion fatigue cracking and numerous other mechanisms. Each failure mode is discussed with regard to boiler location, boiler operation, boiler design, corrosion mechanisms, identification, elimination, special precautions and related problems. Ahnost all failures are preventable through careful chemical treatment and judicious boiler operation practices. Keywords: boiler, oxygen corrosion, deposition, corrosion fatigue cracking, hot water boiler