Why is my Heat Pump thermostat displaying aux/auxiliary heat?

When a system is in defrosting mode, the electric backup within a system (ducted heat pump) will activate in order to compensate for the pause in operation. The outdoor temperature limit of your heat pump could also be reached. Every heat pump has an outdoor temperature limit, where the system can no longer produce heat efficiently. When this occurs, the system
will switch to the electric backup heat to avoid wear and tear on the unit, and continue providing comfort without a drop in temperature. We recommend at -15°C that all systems be shut off, and auxiliary heat activated (with the exception of our cold climate heat pumps), this will assist the lifespan of the unit as it works hardest during colder temperatures. This will also
maintain efficiency of the unit, as at this temperature the cost of opera;on is the almost the same as electric backup.