My 84 F 150 heater will not get hot, what could be the problems?

Did it get hot before since you have had it? If not someone could of bypassed your heater core. As far as the heater core not going bad, they go bad all the time, it is not like it is special for ford parts or anything. Check for any leaks around the fire wall and under your dash. for having a 28 year old truck it is a good thing if that is all you are worried about.

replace thermostat.it is probly stuck open,not allowing collent heat up to operating temp.if your heater core was bad it would be wet on passenger side floor board and your windos would fog up,u would also smell collent.make sure it is full of antifreze,replace the T-stat fill rad,drive until operating temp with defrost on,let cool down,top off with collent,fill the plastic jug with collent up to mark that says full cold.

It is spelled coolant. It is probably the thermostat, that is why I asked is you had COOLANT in your floorboard. It could be an off chance of a hose that is pinched or something crazy, but I would start with the thermostat. Also look around the water pump and see if you can see water stains. Good luck!

try flushing out the rad an the heater core could be blocked preventing the full heat to get out

i personally would check the quality of the coolant, likely its not flowin through the thermostat properly try a coolant flush or change theremostat

if you havent tried anything yet, make sure you even have coolant, the heater will not work if it is too low, also, not knowing where you live, you might just need to put some cardboard in front of the radiator, and if not then maybe it is infact your thermostat