Hercules, QT, Boiler Liquid, Seals and Repairs Cracks and Leaks In Steam and Hot Water Systems, Liquid Formula Will Not Clog Hot Water Coils, Controls, Valves, Or Vents, Forms A Tough Seal That Expands and Contracts With Heat, No Odors, No Priming, No Foaming, Does Not Contain Petroleum Distillates.