With vehicle warmed up and running feel both heater hoses with your hands. If one hose is hot and the other is cold or luke warm, the heater core is plugged. Flushing the heater core should help. If both heater hoses are hot, the temp blend door actuator behind the dash may be broken in which case the entire dash assembly would have to be removed to repair/replace the temp blend door actuator.
Water pump maybe?
not getting heat into cab not even enought to defrost windows i have changed the heater core an thermostat an back washed the core and still nothing
need to know what type of vec. 1992 Mercedes s500 sel
air block in heater hose most likely bleed it
should still be under warranty, could be a bad thermostat.
1st. thing to do is replace the thermostat.
the gas stays on but the water still doesn't get hot
needs a thermostat
you might want to check and see if the heater core is bypassed
thermostat
try a hoter thermostat
why does my 2002 chevy cavalier over heat after i change the thermostat and the water pump