"I have a Janitrol Furnace Model GMP 075-3 Rev B. There are three flame jets.
The first flame jet has the ignitor and the third flame jet has the flame sensor.
Often, when the furnace is triggered by the thermostat, the first jet will ignite,
just fine and the other two will flicker on and off, usually after the third time
all three jets will stay on and the furnace will work as it supposed to. The
Furnace will try three times and will then have to be reset. it seems to me that
a valve may be sticking somewhere."