Apparatus for checking for steam leakage in a steam trap of the kind having a casing with an inlet for steam and condensate and an outlet for condensate, a condensate outlet valve, and actuating means for actuating the valve in the steam trap casing. A probe extends into the steam trap casing in noninterfering relation with the actuating means and responds to the level of condensate in the steam trap casing for changing an electrical condition. A monitor responds to the electrical condition for indicating the condition of the steam trap.