Originally Posted by BayouBiker
The ignition wont even try to light if the sail switch were the issue. Also the Sail switch is a lockout and the system will not retry.
My furnace does try three times when the sail switch is stuck and that has been the case since the furnace was new in 2002 with both stock control boards (2 of them) and with the Dinosaur board installed some 14-15 years ago (still going strong). Each try has the blower on for about 30 seconds followed by a distinct click. The cycle repeats three times before the blower turns off if there is no ignition. I have always interpreted the click to be an attempt at piezo-electric ignition. If the gas does ignite, there is the familiar rumble of the flame immediately after the click.
Of course, newer furnaces with different control boards may function differently.