Why should heat be brought up slowly on a cold boiler?

Bringing heat up slowly on a cold boiler is essential to prevent thermal shock. When a cold boiler is rapidly heated, the outer metal surfaces can expand much more quickly than the inner metal surfaces that are still cold. This differential expansion can create stresses in the material, leading to cracks or other forms of damage. By gradually increasing the temperature, the boiler components can expand uniformly, minimizing the risk of thermal stress and ensuring the integrity and safety of the boiler system. This practice is critical in maintaining equipment longevity and operational reliability.