I have also experienced the same problem. So far i have been able to narrow it down to a tiny wire exposed on the thermistor. Apparently it shorts and then causes the error. when I separate the thermistor it reads correctly and does not show any errors. then the heater heats up to the degree registered in the prontface.
hope this helps. I know this has been a headache for me.
hope this helps. I know this has been a headache for me.