Taz6 Heating issue

Taz 6 is 7 months old. Had issues from the start with bed leveling and then the bed had uneven heating. got these resolved and now I keep getting a heater failure. The nozzle gets to about 190 C and shuts down. If the thermistor is 30W at 24 volts, I should and I do get about 19 ohms on it. What possibly could be causing this to fail? This printer was purchased to print training aides and we have had two successful prints thus far. one of my co-workers bought a much less expensive Ender and has had great success.