Some cars have a sensor in the reserve tank that sticks or the sensor on the engine is gone. Get a manual for you make and it will show the locations.
Make sure you have engine coolant. If the engine isn't getting enough coolant, it will overheat, stall and possibly destroy the engine. One symptom is that no coolant is circulated into the heater. Also check the crank sensor, but check coolant first...then the crank sensor.
Did you make sure that you are putting the themostat in correctly? If you put it in backwardthis can sometimes cause this problem.
A faulty crank sensor would make the engine not run.
Not likely. A bad O2 sensor would illuminate the check engine light and the engine performance would suffer.
Blockage in the cooling system No or little fluid in the cooling system Radiator fan not working
Yes, it won't make the cooling fan turn on even if the fan is fine. If there is a check engine light on and a code for that shows up its possible.
The year, make, model and engine info would help.
The year, make, model, engine info and exactly which sensors you are looking for would help.
Need to know the year, make and engine size of your vehicle.
No.
Try changing the themometer