Quote Originally Posted by seattle_phil View Post
I have an E3D V6 and get "heating failed" maybe once every 15-20 prints. If I reboot the Arduino/RAMPS and rerun the print, it works fine.

I recall reading about this as a Marlin bug that has a fix. Not sure if it's in 1.1.0 RC6 or not, I know it's not in RC3 (what I'm running now).
Running RC8, but I have been running that for a while now and am only recently getting the issues. Watching my temp during a print, it seems to vary +/-10 degrees.