Since you already replaced the thermistor and we will assume that it is good, then the other failures that would cause this error code would be a wiring problem or a failed electronic control board.
unplugging the dryer
and checking the wiring connection of the thermistor to the electronic control board. The thermistor attaches to the control board on the P2 connector (red/white and black wires on pins 5 and 6). The image below shows the procedure for accessing the control board in this dryer. If the connection is okay, pull the connector off of the control board and check the resistance through the red/white wire and black wire with a volt/ohm meter (with the dryer still unplugged). You should measure about 10K ohms (10,000 ohms) at room temperature. Make sure that your meter is set to the proper range. If you read infinite resistance (open), then you could have a wire harness connection problem between the control board and the thermistor. Check the resistance across the leads of the thermistor (with at least one wire removed from the thermistor). If you measure normal resistance (10K ohms) at the thermistor, then you will need to repair the wiring connection between the control board and the thermistor.
If you measure the proper resistance through the thermistor circuit at the connection to the control board (red/white wire to black wire on the P2 connector), then the electronic control board is bad and will need to be replaced.
If you need more help with this dryer problem, resubmit your question with additional details and the full model number of your Duet dryer.