2006 Infiniti G35 No Heat in motion

My car was in an accident. Part of the repairs was to replace the radiator and mount. Since getting the car back I have no heat unless the car is in motion, then it works fine. The first thought was an air pocket. The antifreeze was removed and put back in under pressure 4 times. Now they have replaced the thermostat and taken the heater core apart and cleaned that. The core was found to be in good shape with minimal deposits. The heat and AC worked fine before the accident. I questioned the shop on antifreeze type and mixture ratio. Only negative was that distilled water was not used but I have been assured the proper Glycol antifreeze was installed. The car has been in for a week to try to remedy this problem and no luck. Do you have a suggestion? We have fairly harsh winters and I cannot even warm the car up since it is sitting still. Makes a remote start useless.