Display reads higher than normal and does not match other dew point equipment:

 

If soot is allowed to collect on the dew point sensor in the instrument, it could result in higher readings. This soot will also retain moisture than can corrode the sensor over time. Change the filter element if it is possibly saturated with soot. 

Also, the dew point sensor tip can be cleaned by carefully removing it from the sample block (see Section 2.0 of the Field Calibration instructions) and rinsing it in isopropyl alcohol. The power should be off while this is done, and the power should remain off for at least 30 minutes after this procedure to allow all of the alcohol to completely evaporate.