When your thermostat shows AUX with a red light, your heat pump's electric backup strips are running. This kicks in automatically when it's below 40°F outside. It's normal and nothing to worry about.
If you see the thermostat go to AUX and that red light pops up or it's flashing, that just means the heat strips are on. It's nothing to worry about. It's normal. It's fine. It's really a backup heat source because once it gets below 40 outside and you have a heat pump, it needs help. So that's why you have those heat strips to kind of give a hand to add heat.
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