Also, make sure in the last step of the programming you are making sure it is set to "H1". That is the heater setting... If it is set to "C1" then the t-stat thinks it is running an air conditioner. So if the temp is set to 90 deg and the room temp is 80deg the t-stat thinks it is cool enough and will shut off till the room temp reaches 90 deg. At which time the t-stat will turn on what it thinks is an a/c but in reality will be a heater, and that is where it can get ugly...