03 eclipse problems

Just got done changing a cracked radiator.new one is in but now have another problem.coolant isnt moving through the block.Top hose off the radiator is geting hot but the bottom hose is still cold.went out the next morning.both hoses were flat.thought maybe vapor lock.cant find the air bleader.did it the old fashined way.but now the coolant still isnt moving.car has no heat.starts to run hot when idle but cools off when hold it around 2500 rpm.Anyone have any ideas???????All help is welcome

Update.Put new Thermostat in tonight.same problem.coolant isnt moving through the block unless your running at a high RPM.heater starts blowing hot air,and car starts running normal.thinking it might be the water pump..

Thermostat? That is pretty cheap and easy.

Did you burp the system?