THis is first cold spell of season and I cannot rember last year.
I have very short term memory.
The thermostat is set on 69. Temp outside is about 10 F.
Temp inside is only about 66. Heat pump runs constantly.
ONly time time tries to go up is during defrost cycle with emergency heat on.
When the outside temp drops below the "thermal balance point", which is the outdoor temp at which the heat pump can no longer keep up on its own, then the t-stat brings in aux heat. The aux heat has a different set point on the t-stat than the primary heat, and is usually 2 or 3 deg lower.
When the indoor temperature gets up to 66 or 67 deg, then your aux heat drops back out becuase that is the aux heat's set point on the t-stat. The heat pump can't keep up with the demand without the aux heat's assistance, so the heat pump runs continuously while the aux heat cycles on and off. When the outside temp rises above the thermal balance point then the heat pump can finally keep up on its own, so the indoor temp rises to the 70 deg setpoint and the unit finally cycles off completely.
That's normal heat pump operation. In other words, if you want 70 deg in the house when it's below freezing outside, then set the t-stat on 73 deg. When it warms up outside then set it back down to 70 deg. This 2 or 3 deg swing in indoor temp is a common complaint with heat pumps. The system can be modified to prevent this from happening, but this isn't something that you'll probably be taking on yourself. In fact, even some techs would give you a blank stare if you asked them to modify your system to prevent this swing from happening. Most people, once they understand that this is normal heat pump operation will learn to live with it.