York (Model: P4HUA1ZN06401B) vertical natural gas furnace. Observed that the burner on right, by the glowing starter, starts properly but the other three burners do not light and since the thermocouple on the left does not start, the gas is stopped in about 5 tyo 10 seconds. I cleaned all four nozzels and it did not help. I find that if I blew slightly into the combustion chamber when it was attempting to start and the other three burners started and continued to burn until the thermostat was satisfied. Note: The combustion blower fan is operational.