A heating boiler must have a permanently attached marker indicating:

A heating boiler must have a permanently attached marker indicating the lowest permissible water level for several important safety and operational reasons. This marker serves as a critical reference point for operators to ensure that the water level within the boiler does not drop below a safe threshold. Maintaining the water level above this point is crucial to prevent the boiler from overheating and potentially suffering damage or failure.

If the water level falls below the lowest permissible level, the boiler may expose boiler tubes or other components to direct heat from the burners, leading to overheating and possible rupture or explosion. By clearly marking this level, operators can quickly and easily ascertain whether the boiler is operating safely, thereby preventing accidents and ensuring the longevity of the equipment. Additionally, adherence to this safety standard is a regulatory requirement in many jurisdictions, emphasizing the importance of maintaining safe operating conditions in boiler operations.