Why is my TH1100DH/TH1110DH/TH1210DH showing an error message HI? What does it mean?

HI = The ambient temperature is above 122F (50 degrees C). Remember it can take several hours for a newly installed thermostat to normalize to room temperature. If the room temperature is lower than 122F (50 degrees C) and the thermostat is still displaying HI replace the thermostat.