If your car is in fact a E230 you must be outside USA. If it is a typo and your car is a E320 you are probably in the USA.
Depending what year your car is and if your car has USA specs, most heating problems are related to a bad thermostat, coolant temperature switch (are your auxiliary engine fans working?) and the engine fan.
When was the last time you change the coolant? Is your AC working fine?
These are things you should look into. The thermostat and the coolant change are the cheapest...