Nissan Repair: NO PRESSURE IN COOLING SYSTEM, nissan 200sx, radiator cap

Question
Hi Von,
I currently have no heat in my Nissan 200sx even if it has been running for 30 minutes. I checked and changed the thermostat but noticed that there is no pressure in the cooling system. The liquid in the hoses is only warm. Also the water pump system in turning well with the belt. What could be the problem?
Many thanks!
Nicolas

Answer
If you alreaady changed the thermostat I would be looking at getting a new radiator cap.  You need pressure to make the system work.  Also, you did not mention if you flushed the system when you changed the thermostat.  If the coolant leaked down enough you could have air in the system preventing the heater from getting coolant.  If it were me I would buy a new radiator cap.  Also, I would check for an air bleed screw at the firewall connections to make sure there is no air in the lines to the heater core.