A couple of days ago I noticed that my American Standard Freedom 80 was not working properly. The furnace burners would ignite for about 10 seconds then go out. This would repeat about 5-6 times. After the last ignition attempt it would lockout but the fan would then start and circulate unheated air throughout the house. I left the system on and went to bed. During the night the burners did end up igniting and the furnace worked as normal until the morning. But then in the morning the ignition issues happened again. There was no heat the entire next day, but then ignited again at night while I slept. On the third day the furnace worked fine with no issues. On the fourth day, back to the same ignition problems. Anybody have any ideas of what could be the issue?