Haier cpn10xh9 heater won't stay on. uni...

The heater won't stay on and unit turns itself off. Sometimes when in heater mode the unit won't even turn on at all. There's nothing in the manual that says if the unit should be vented outside the window when using the heater mode like you do when using it in the air conditioning mode, so I do still have it venting out the window. This is a combo air conditioner / heater / dehumidifier.