Found this thread whilst researching heater issues. I was perusing the Xfire shop manual and it states:

"The coolant circulation pump (5) serves for maintaining a uniform flow of heating water through the heater core (4) even at low engine speeds and in the residual engine heat utilization mode (REST)"

I've been testing mine because I don't think it's pumping well (my heater is not getting very warm) and on my car it's running whenever the engine is running and the heater is on (which confirms the description above).