I have a Profilux II Plus and PT 1000 temperature sensor. The sensor shows temperature of +20.0C +-0.3C regardless of what the temperature actually is. I've placed the sensor in hot water and cold water and the temperature is always between 19.7-20.3C. I bought the item used a few months back and it worked normally for the previous owner. I thought the sensor might have broken when I moved it in and bought a new one, but it shows exactly the same temperature! Is it my Profilux that is actually broken, or is there some other explanation for this "getting stuck at about 20C"?

Recalibrate? Return factory settings? What should I try?