A furnace will not turn off on its own. The main reason it doesn’t turn off is that the pilot light that controls the switch is shorted out or burnt out. A pilot light is attached to a circuit breaker panel and when it gets hot, the pilot light will signal the circuit breaker to kick in. The circuit breaker then throws a signal back to the furnace telling it to turn off. When the pilot light is burnt out, either the duct system is clogged or the heating coils need to be replaced, or both.
If the pilot light is burnt out or the furnace gets very hot, the system will turn itself off to conserve energy. On the other hand, if the pilot light is shut off, the pilot light usually only lasts for about fifteen seconds and the pilot light circuit breaker senses that the pilot light is off and shuts the breaker off. If the pilot light stays lit, the circuit breaker resets and then tries to kick in again. Then the cycle continues as before. It is possible that the pilot light was replaced or the system was repaired recently, therefore the pilot light may be burned out.
Replacing the pilot light can be done by yourself if you know what to do, or the job is done by a professional company that does this work. If the pilot light is not replaced, or there is an electrical fault on the furnace, it’s not worth the time or expense to change the pilot light. There are many different ways of accomplishing this task, but it should only be done by a professional. It is not recommended to try to replace the pilot light yourself. You could end up damaging the furnace, which is not good because they last so long.