Abstract: The invention relates to an apparatus for quickly and inexpensively plugging leaks in the tubing of low pressure steam boilers. The invention uses a cap containing a gasket channel of the same diameter as the edge of the tube. The underside cylindrical wall of the cap contains an aperture in common with that of the top of the cap. A threaded rod is passed through the cap and connected to an identical plug on the other end of the tube. Simultaneously tightening hex nuts on the two rods seals the tubing ends.