Auto, and that switch only controls the fan.
Could be a few things, the house being cold, a broken temp sensor, disconnect between the sensor and the furnace/pump.
The exact same thing it does in the cooling mode, the change between modes of operation does not take place in the compressor.
No.
By using the ground as the source for heat, much like an airsource heat pump uses air to remove the heat from the air on a cold day a geothermal system using the more consistent earth as the source...