My new E3Dv6 was working great for about a week before it started having some intermittent issues. The readout of my RAMBO controller would sporadically drop to ~7 C (from ~21 C room temp) before erroring out the controller board. When this doesn't happen, the thermistor read-out seems to max around 165 C, but the hot end is much higher based on the viscosity of the plastic extruded. I would guess > 250 C. What's my best shot at troubleshooting this issue? Should I jump straight into thermistor replacement?