My armstrong Ultra V Tech 80 furnace suddenly doesn't want to ignite. Please bear with me as I don't know a whole lot about furnaces. I can hear and see the gas come on, but it does not ignite. I can hear a clicking noise I assume is the ignitor trying to engage, but the furnace doesn't start. It tries to ignite twice in a row and then stops for awhile. It did start one night on it's own, but has since quit on me. I changed the filter less than a month ago and the furnace is four years old. I appreciate any ideas or guidance anyone can provide before I resort to calling a professional.

Thanks,
Liza