Switch problem? Cables disconnected?
it has a partially clogged heater core.replace the heater core
thats it i think
open or missing thermostat
Because the resistor between the heater swithch and the heater motor is not functioning. Usually mounted on, in or near the heater enclosure. Its a common repair, and can be done by the do-it-yourselfer.
First thing to check is the coolant level. It can be low and keep the heater from getting warn and still not make the car overheat. If it's full, too cold a thermostat. Worst case is a partially clogged heater core. A collapsed heater hose possible.
you need a new blower motor resistor
low on anti freeze or blockage in heater coil
probably the resistor pack on the evaporator case.
The water level in the radatior is lower than the inlet of the heater core. At idle the water flow is not high enough and the air bubble in the cooling system moves to the highest point in the system The heater core, Now hot water, no heat Check your thermostat, when the car is sitting still it may not be getting the cerculation it needs
To unblock the heater core, remove two heater hoses coming off of the engine going to the heater core. They are usually located on the passenger side of the vehicle near the firewall. Then use a high power water or air source to blow through the lines both ways.
Could be, low on coolant, stuck open thermostat, plugged up heater core, faulty temp blend door actuator,