When installing the Camstat thermostat, make sure you set the proper mode for your system. The Camstat supports 15 modes. Setting the incorrect mode may cause your system to not operate properly (on heat pump systems, the compressor and heat may run at the same time). Refer to the instruction sheet on how to set the proper mode. The thermostat ships preset to mode 15, which enables all modes. This most likely not the mode you want to use.