Minnesota Boiler License Practice Exam

What is the purpose of the low limit control on a hot water boiler?

1. A low limit control is not used on a hot water boiler

2. Will not allow the burner to leave low fire position until the temperature reaches 150 degrees Fahrenheit

3. A low limit control will reduce pressure on the hot water system

4. A low limit control will reduce pressure on the recirculating pump

The correct answer is: Will not allow the burner to leave low fire position until the temperature reaches 150 degrees Fahrenheit

The purpose of the low limit control on a hot water boiler is to maintain a minimum water temperature within the system to prevent issues such as overheating and excessive expansion or contraction that can damage the boiler or related components. By setting the low limit control to a specific temperature, such as 150 degrees Fahrenheit, it ensures that the burner does not go to a lower fire position until the water temperature reaches this threshold. This helps in maintaining efficient operation and extends the life of the system by preventing the burner from operating at low temperatures where it might not combust the fuel properly, potentially leading to incomplete combustion and other operational issues. The other options do not accurately depict the function of the low limit control; it is not that it is typically absent from hot water boilers, nor does it directly reduce pressure in the system or the recirculating pump. Instead, its primary role is temperature regulation, which ties back to the performance and safety of the boiler operation.