Abstract: The following substitute specification does not contain and new matter as that submitted in the Provisional Patent Application No. 61/018,908 filed on Jan. 4, 2008. The boiler plug system of the invention is intended for plugging leaks in the steel tube flue gas-to-water heat exchangers of steam boilers. The boiler plug of the invention is adaptable to the varied sizes of heat exchanger tubes. In this specification, the elements of the invention will be described as applied to two (2) inch ID (inside diameter) steel tubing heat exchangers with the understanding that the boiler plug of the invention can be made smaller or larger as the particular application may require. The boiler plug of the invention is readily adaptable to heat exchanger tubing of one and one-half (1.5) to three (3) inch ID. The boiler heat exchanger panel consists of a closely packed bundle of lengthy steel tubes having a diameter of about two (2) inches.