Printer stutters to a halt and shuts down...?!

Testing this new build dual head printer.

Things are going fine during the Dual extruder test print, when the machine suddenly starts juttering momentarily then stops.

Pronter face shows the hotends have now shut down. (getting cold)

No indication of a problem on pronterface and all comunications to the printer are ignored.

I have to reset printer to regain control.

Anyone seen this before?

I had set-up an electric heater as my basement was getting too cold to print in.

Unfortinatly, when it cycled the heater on/off sometimes one of my printers would hick-up and go offline.