Braeburn Thermostats I Have A Recently Installed "Braeburn 3000" Electric Heat Pump Thermostat-which Will Not Operate The Heat -but

I have a recently installed "Braeburn 3000" electric heat pump thermostat-which will not operate the heat -but - braeburn thermostats

AC worked fine all summer, because if it was installed, there is a method, since in order to diagnose the problem?