Free standing Vulcan gas heater about 5 feet tall heat blows out the bottom quite old red light comes on at start then unit gets very hot and turns itself off

SOURCE: vulcan space heater lighting instructions

turn the round knob to left "the ignitation" spot, then push down the button to light the pilot.

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you have a couple of problems first of all your drivers sd=ide heated heat pad is probably faulty, for your heating problem you may have to get the hvac doors recalibrated.

SOURCE: gas heater doesn't stay on longer than 5 minutes.

It sounds to me that your air flow is restricted somewhere. The first thing to check is your air filter. If that gets real dirty your restricted air flow will cause the hi-limit(hi temperature limit switch) in your heat exchanger compartment to over heat and open up your gas valve electrical circuit,thus, shutting off the gas to your burners. After the hi-limit switch cools down the furnace will go back to heating again then it will overheat again(you get the picture?) If it keeps cycling on and off like that the house will never get warm if it is cold outside. If your air filter is reasonably clean(you should be able to see light thru it easily) then the secondary heat exchanger could also be dirty, this is located above the indoor fan housing, you would need to pull the indoor blower assembly out of the furnace and look up above. The secondary heat exchanger looks similar to a radiator will fins. You can use a medium stiff plastic brush to brush the dirt,hair, whatever off of it. Another problem spot would be the cooling evaporator coil (if you have central airconditioning) located most likely above the furnace in the plenum(if your furnace is in a basement). This usually is difficult to access if an access cover wasn't installed when the airconditioning was installed. I would recommend an experience service tech to clean it for you. Also make sure all you supply air registers and return air registers are open . These are the things I would check first. Good luck!!

SOURCE: pilot on, gas fires up, no fan comes on.

Sounds like you are talking about the indoor fan that circulates air through house. Turn the unit off and make sure the fan rotates freely. Next check the capacitor for the fan. If it looks swollen its probably bad. If it doesn't look swollen then you will need a multimeter to check it with. If that's ok then check the fan relay. Let me know what you find.

SOURCE: we have a Vulcan Ultra high efficiency gas ducted heating

Gas ducted central heater won't switch on all of a sudden