Could be a clogged heater core. Just because it doesn't leak doesn't mean it's working right.
I would say that you are losing coolant somewhere hoses,water pump,radiator.
may be your heater control valve
Check to see that the heat control is working, and water is flowing through the heater core. Make sure that the engine thermostat is not stuck open, and the engine coolant is full.
there is no heat inside the car what is wrong ?
Thermostat possibly stuck open. Another possibility is the heater core is clogged. I would recommend you perform a complete cooling system service. Drain and flush the system with the heater set to high. Replace the thermostat, and install a 50/50 mix of coolant and distilled water. Bleed all air from the system.
the fan is working but no heat
Old ducts not working properly, blocked or collapsed ducts, or vacuum problem not allowing passages to open
THE COLD AIR WARM AIR EXHANGE DIVERTER DOOR IS NOT WORKING
There is no heat in my 97 buick park ave. why? the fan works an ac. an the temp says 90 degrees but still comes out cold.
heter not working on 2006 gto . i do have air ,but no heat.