FloorStat 500650 GFCI Test

[jmaxwell]

I have the floor heating controller listed above.  It has worked perfectly for 8 years and recently stopped warming the tile floor.  I attempted to conduct the GFCI test, but am not sure about this.  It references the "Test warning light", but I don't see any light when I press the Test button.....and further, am not sure where this light is located....does the "backlight'" appear on this test or is there another light somewhere, and if so, where is it?  Is it likely that the controller has died, or is this problem more likely an indication of a short in the floor wiring.....and how would I check to confirm the problem?
Tired of wearing socks in the bathroom.
Thanks for your help.

[btwhitehurst]

The light is pretty obvious when the GFCI is tripped. You may be at an "END OF LIFE" situation in that stat. All GFCI are built with a life span so that you have to replace them to keep them in good working order as per UL943. The 500650 is a discontinued stat. We at Pexheat.com still have a couple of the 500750-HB left in stock but it is discontinued as well. The current thermostats are the 500850 and 500875.