Amit:
When I did a coolant flush on my 97 C230 last week I drained the coolant from the radiator via the valve at the bottom of the radiator, and drained the coolant from the engine block via a special drain bolt on pax side of hte engine.. draining was done with engine warm and the heater "on"..

Replacement of the coolant > closed all valves > added coolant > squeezed the hoses to force coolant through the system.. and kept adding coolant till it would not accept anymore > started engine got it up to operating temp... system seemed to push air out of the system..

heater on >> it has heat..