Heater issues

confused. have a Ram 3500 diesel that is not putting out any heat. think it might be heater core but also checked for water flow but not getting any but engine is not overheating very confused figured if thermostat was bad and no flow would overheat any suggestions

Check inlet and outlet temps of heater core they should be very much the same, hot. If not heater core might be restricted and needs to get back flushed or replaced. If both cold might check the heater valve operation. If not might be the controls and blend doors in the duct work themselves. How and where are you checking coolant flow?

The coolant temperature gauge on the instrument panel should show 190F after the engine is warmed up.