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AD7689 unipolar differential pair problem

Hello, everyone. I am trying to measure thermistor voltage to check the temperature.

In this case, I have designed a circuit like the above one, and I connected 2 wires to AD7689's IN0 and IN1.

The VTH(+) is connected with IN0 and VTH(-) is connected with IN1.

As I wanted to measure the voltage between the thermistor, I set AD7689 operates as unipolar differential pair.

The set value is INCCx = 5, INx = 0, SEQ = 0,  REFx=0. And I think it is correct but the measured voltage was totally wrong. 

E.g, When I put the thermistor on the hot place and checked its voltage by using a multimeter, its value was 0.7V but ADC value was 22263 (0.849V)

Moreover, when I have put the thermistor in the cold place, the ADC value was still 22263 although the voltage was changed to 1.3V.

I think I did something wrong when I set the AD7689 but I can't understand what I did wrongly.

So please help me!!!