What safety control protects a steam boiler if the condensate pump fails to return water to the boiler?

The low water cut-off is a critical safety control designed to protect a steam boiler from potential damage caused by low water levels. When the condensate pump fails to return water to the boiler, the level of water in the boiler can drop to a dangerous point. The low water cut-off serves as a safeguard by continuously monitoring the water level within the boiler.

If the water level falls below a predefined threshold, the low water cut-off automatically shuts down the boiler. This action prevents the boiler from operating in a low water condition, which could lead to overheating, boiler tube damage, or even catastrophic failure due to insufficient cooling and steam generation capacity.

Other controls, such as high pressure limit control, low pressure limit control, and flame safeguard control, serve different purposes related to pressure and flame monitoring, but they do not specifically address the scenario of low water levels resulting from a pump failure. Hence, the low water cut-off is specifically designed for the exact situation described in the question, making it the correct safety control for protecting the steam boiler under these circumstances.