My heater in wont work

are you installing the correct thermostat the right in the head or block
3 thermostats indicate incorrect fitment method
heater hoses run either way as the water is pushed through the heater core by the pump

You mean the car is running fine but just No Heat?
If so
-Sound like the heater hoses are plug. or the control valve is no function

-Check the heater control valve and flush the heater unit with water of garden hose from both directions.
Q: How do I know that is working or not?
A: Slide the heater control from Hot to cold or cold to hot and check it turn or not. (If not turn at all. The cable is broken or slip off)

Mai Lor

Thermastat and heater core.

Check the thermastat or your cooling fan to make sure all is working good. If your engine cant warm up, you will not produce any heat inside the car

have you checked the fans to make sure they are turning on? how about your coolant level?

This could be that the actuator that opens the door in the heater is dead.. or the actual heater-core is bad. Which is costly and expensive.

the thermostat should be closed when you take it out, therefore the thermostat is bad. It does not closed.

make sure there is enough anti-freeze in the truck and if it be a while flush the system and replace thermastat and check all the fuses for the blower and if they are good and the power going to the blower is but none is coming from the blower replace the blower itself

I don't know if there is a bypass valve but the heater core could be all clogged up not letting water flow through it.

Blend door motor or blend door could be stuck. ...accordianman