An electrode probe assembly for monitoring and finding fault in the glass lining of metal vessels, pipes or the like, characterized by a cup-shaped electrode with an insulated stud inserted through a hole in the wall of a mounting member. An insulating gasket insulates the electrode from the member. Resilient means bias the cup-shape electrode against the gasket preventing leakage due to shrinkage of the gasket. Electrical connection of an insulated circuit is made to the stud.