The Hartford loop will:

The Hartford loop is a design feature used in steam heating systems to ensure the safe operation of the boiler, particularly in preventing a dangerous situation where the water level in the boiler drops too low. The primary function of the Hartford loop is to connect the steam pipes to the return lines in a way that maintains a minimum water level within the boiler. By doing this, it ensures that there is always some water present, which is crucial for cooling and protecting the boiler from overheating or damage due to low water conditions. This is particularly important in preventing accidents such as boiler explosions, as the water level needs to be maintained above a specific safe point to ensure proper operation.

The other options do not accurately define the function of the Hartford loop. It is not specific to multiple-boiler systems, represents more than continuous circulation, and does not replace any components such as a feedwater check valve. These elements clarify the specific role of the Hartford loop in enhancing the safety and efficiency of steam heating systems.