I have an older T300P that I bought used. It will run for awhile, sometimes for a few hours and then shutoff. There will be a fire in the burnpot and it appears to be feeding pellets and the blowers will just shut off. I havecleaned the photoeye (old style). If I try it at the 3 different feed rates, it will seemingly run longer on a higher feed rate and the shortest on the lowest rate. Could this be a high limit switch problem or something else??