[jsb5717]

If the furnace is attempting to ignite, meaning you can hear the igniter clicking, then the sail switch is working correctly. If your furnace isn't trying to ignite then there are are a couple possible causes:

Sail Switch - this is the easiest thing to check first. It's easy for a bit of lint to get sucked into that switch, preventing it from closing and allowing ignition. After a few attempts it is possible for it to clear. But it's 2 screws and 2 wired connectors to remove and check it. Make sure it's clean. Since it currently sounds like an intermittent issue I would suspect the Sail Switch.

If the Sail Switch is clean then it could also be your control board