To tell if it's the sensor or board you will need to test the temp sensor at room temp with an ohm meter.
1. Disconnect the power
2. Gain access to the plug for the temp sensor
3. Disconnect the sensor plug
4. Take an ohm measurement across the two wires for the sensor.
The reading should be around 1.1k ohms (may read 1100)
If so, your sensor is likely good. If not, it could be a bad connection either at that plug or at the board. If the connections are good, most likely it would be the board. Not the touch panel, but the control board.
If it's discontinued, it leaves you with the option of having the board sent off to be rebuilt.
I hope that helps.