thermo-pride furnace cuts off

Help. I started up my good old furnace after a) checking for water b) blowing out the fuel lines c) cleaning the strainer d) breaking down and cleaning the pump e) cleaning out the blower blades f) lubricating the motor and g) replacing the burner nozzle with the right size, with the electrodes adjusted for the right angle. What I get is a silky smooth start that runs the timer limit and shuts off. Big pretty flame, steady oil stream. What tells it to stop? The blower never comes on but when I run it manually it makes no difference. Same cut off, same time.
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