Re-read your post... It does seem like its a thermocouple issue, but if not and the stove is good and clean, it appears its a board issue or wiring issue. I know boards are expensive, sometimes you can have it checked by your local dealer in a stove they have. But, if stove tries to go through startup (by feeding when reset button is pushed and ignitor lights off pellets, its waiting for the next gate 200 deg flame sense from the thermocouple), at that point its the TC, board or wiring. It certainly seems like its a TC issue. I don't remember the Millivolt numbers the TC generates for 200 and 600 degrees though. The board needs to see that MV reading as a positive voltage too. Good luck.