Final answer:
The purpose of a limit control in a boiler is to maintain the water level.
Step-by-step explanation:
In a boiler, the purpose of a limit control is to maintain the water level. The water level in a boiler needs to be carefully controlled to ensure the safety and efficiency of the boiler.
If the water level gets too low, it can expose the boiler's heating surfaces to overheating, while if it gets too high, it can lead to water carryover and damage the steam distribution system.