When the outside air temperature drops below 4 – 5 °C, your heat pump may go into defrost mode.
It may also make an unusual sound when this mode is activated. In this mode your heat pump may not appear to be pumping out hot air. If this is the case, it is best to leave the unit alone until it has gone through this cycle. If you know it is going to be cold and frosty overnight, you can be sure your system will go through at least one of these cycles. The colder the temperatures that a heat pump operates at, the more often defrost cycles must occur. The unit is removing frost and ice buildup, in order to run as efficiently as possible.