maxtemp error reads 836/0

I have just finished assembling my printer. During the setup and testing I get a max temp error of 836/0. When I unplug extruder sensor wire it then read -19/0. It also won't let me set the nozzle temp. I try to set the nozzle to 270, but won't start to heat up, it just returns to zero. The bed temperature does the same thing. Is this a firmware problem or a wiring/solder problem.

Determined the problem. The set screw holding the wires in the extruder was too tight and pinching the thermistor wire and changing the resistance the board was reading.