Topper
Even if the thermostat says that the room temperature is correct that does not mean that their are not local drafts near the vent.
I would also take a look at the siting of the end of tube temp sensor as has been mentioned above. If this is being heated by an over head heater of an incubator it will say that the end of hose temperature is correct and turn down the hose heater causing rain out.
Robert
