Assuming you have checked the water and its topped up, could be thermostat blocked.
There could be multiple reasons why a heater would stop working in a truck. There could be low coolant or a bad fuse to make a heater stop working in a truck. The best way to find out the reason is to take it to a certified auto mechanic.
Yes it will stop heating up...........
Could be low on freon,
There are a couple of reasons why a 1999 Oldsmobile Alero ac heater to stop working. The heater coil may need to be replaced or the HVAC blower motor may need to be replaced.
Possibly a relation to the blower motor/ heater door accuators.
yes
The blower may simply have burned out. If the blower is out then the heater probably still works.
Need to know what it is not doing, post more info.
heater core
Heater coil
If you have lost a sufficient amount of coolant this will stop the heater working because there will be no hot water in the heater rad.
The heater on a Mercedes c200 will stop working if the heater core is blocked. It allows hot coolant from the engine to be used in heating the cabin.