From RKI - 

The Leak Check Mode is now a standard feature on all GX-Force units shipped from RKI.  This mode adds a ppm-level combustible leak check function to this sample drawing 4-gas monitor. 

The Leak Check Mode is included with all GX-Force units, but it is turned off by default.

If your existing unit is not set to Leak Check Mode, click here for instructions on how to add the Leak Check mode to previously shipped instruments. 

TG Technical Services carries RKI gas detection instruments and would be happy to assist you with any questions you may have about the GX-Force gas detection instrument or any other gas detection product you may be interested in.