Repetier and extruder temp

So, sometimes when I pull a print off the print bed and go to send my next print (sometimes 10 minutes after or some times hours later) the heatbed heats up, but the extruder just continues to drop in temperature even though it shows that the "heat on" is lit up for the extruder. Some times I need to shut off, and unplug the printer for a few minutes to get it to heat up the extruder. Any thoughts?

 

robo posted a new version of the marlin firmware, i would upgrade to it. then see if the problem still exists.